feat: persistent settings + server sync + language selector

Settings now persist across app restarts via SecureStore:
- Theme (KaizenThemeId), appearance (Light/Dark/System), username, locale
- All loaded on SettingsViewModel init, saved on every change

Server sync: fetchMe() returns name + email from /api/v1/me,
populates SettingsViewModel on login and each foreground resume.

Language selector: System / Deutsch / English pill toggle in Settings.
Locale preference stored; runtime switching deferred to next iteration.

MeResponse expanded to parse name + email (was defaultModel only).
SettingsViewModel tests updated for store-less default state.

CLAUDE.md

@@ -94,6 +94,15 @@ Full spec: `DESIGN.md`. Branch: `feature/design-system-v2`.
 - ChatModels: `Suggestion.labelRes`/`promptRes` and `ChatMode.labelRes` are resource IDs (Int), not hardcoded strings.
 - `ModePillsRow`: `selected` state is `Int` (resource ID), not `String`.
 
+### Settings persistence + server sync
+
+- **SettingsViewModel** takes `SecureStore` — theme, appearance, username, locale survive app restart.
+- Theme selection persisted as `KaizenThemeId.value` string ("amber"/"blue"/"mono"/"aurora").
+- Appearance persisted as `AppAppearance.name` ("Light"/"Dark"/"System").
+- On login + on each foreground: `KaizenApi.fetchMe()` → `MeResponse(name, email, defaultModel)` populates SettingsViewModel name/email.
+- **Language selector** in Settings: System / Deutsch / English. Stored as `locale` in SecureStore. Note: currently only stores the preference; runtime locale switching (AppCompatDelegate.setApplicationLocales) needs wiring in MainActivity on next iteration.
+- No server-side theme storage — web uses localStorage, app uses SecureStore. Both are client-local.
+
 ### Offline-first cache layer (Room) — added 2026-06-21
 
 Architecture decision document: `OFFLINE_CACHE_ADD.md`.

app/src/main/java/dev/kaizen/app/MainActivity.kt

@@ -31,8 +31,9 @@ class MainActivity : ComponentActivity() {
             window.colorMode = ActivityInfo.COLOR_MODE_WIDE_COLOR_GAMUT
         }
 
-        val settingsViewModel = SettingsViewModel()
+        val secureStore = SecureStore(applicationContext)
-        val sessionViewModel = SessionViewModel(SecureStore(applicationContext))
+        val settingsViewModel = SettingsViewModel(secureStore)
+        val sessionViewModel = SessionViewModel(secureStore)
         val chatViewModel = ChatViewModel(applicationContext)
 
         // auto() picks light/dark system-bar icons based on the system theme

app/src/main/java/dev/kaizen/app/chat/ChatScreen.kt

@@ -158,6 +158,10 @@ fun ChatScreen(
             }
             is FetchResult.Fail -> errors.add(r.reason)
         }
+        KaizenApi.fetchMe(cfg.baseUrl, cfg.token)?.let { me ->
+            me.name?.let { settingsViewModel.updateUserName(it) }
+            me.email?.let { settingsViewModel.updateUserEmail(it) }
+        }
         chat.conversationRepo.refresh(cfg.baseUrl, cfg.token)
         if (errors.isNotEmpty()) {
             loadError = errors.joinToString(" · ")

app/src/main/java/dev/kaizen/app/net/KaizenApi.kt

@@ -23,7 +23,11 @@ import java.util.concurrent.TimeUnit
 
 @Serializable private data class TokenRequest(val email: String, val password: String, val name: String)
 @Serializable private data class TokenResponse(val token: String)
-@Serializable private data class MeResponse(val defaultModel: String? = null)
+@Serializable data class MeResponse(
+    val name: String? = null,
+    val email: String? = null,
+    val defaultModel: String? = null,
+)
 @Serializable data class WireMessage(val role: String, val content: String)
 @Serializable private data class ChatRequest(
     val model: String,
@@ -164,6 +168,22 @@ object KaizenApi {
         }
 
     /** GET /api/v1/me — resolve the user's configured default model (best-effort, null on any failure). */
+    suspend fun fetchMe(baseUrl: String, token: String): MeResponse? =
+        withContext(Dispatchers.IO) {
+            val req = Request.Builder()
+                .url("$baseUrl/api/v1/me")
+                .header("Authorization", "Bearer $token")
+                .build()
+            try {
+                client.newCall(req).execute().use { resp ->
+                    if (!resp.isSuccessful) return@use null
+                    json.decodeFromString<MeResponse>(resp.body!!.string())
+                }
+            } catch (e: Exception) {
+                null
+            }
+        }
+
     suspend fun fetchDefaultModel(baseUrl: String, token: String): String? =
         withContext(Dispatchers.IO) {
             val req = Request.Builder()

app/src/main/java/dev/kaizen/app/net/SecureStore.kt

@@ -77,6 +77,20 @@ class SecureStore(context: Context) {
         }
     }
 
+    // ── Settings persistence ─────────────────────────────────────────────────
+
+    fun loadThemeId(): String? = prefs.getString(KEY_THEME_ID, null)
+    fun saveThemeId(id: String) { prefs.edit().putString(KEY_THEME_ID, id).apply() }
+
+    fun loadAppearance(): String? = prefs.getString(KEY_APPEARANCE, null)
+    fun saveAppearance(mode: String) { prefs.edit().putString(KEY_APPEARANCE, mode).apply() }
+
+    fun loadUserName(): String? = prefs.getString(KEY_USER_NAME, null)
+    fun saveUserName(name: String) { prefs.edit().putString(KEY_USER_NAME, name).apply() }
+
+    fun loadLocale(): String? = prefs.getString(KEY_LOCALE, null)
+    fun saveLocale(locale: String) { prefs.edit().putString(KEY_LOCALE, locale).apply() }
+
     fun clear() {
         prefs.edit().clear().apply()
     }
@@ -89,5 +103,9 @@ class SecureStore(context: Context) {
         const val KEY_SPEED = "speed"
         const val KEY_FAVORITES = "favorite_models"
         const val KEY_MODELS_CACHE = "models_cache"
+        const val KEY_THEME_ID = "ui_theme"
+        const val KEY_APPEARANCE = "appearance"
+        const val KEY_USER_NAME = "user_name"
+        const val KEY_LOCALE = "locale"
     }
 }

app/src/main/java/dev/kaizen/app/settings/SettingsScreen.kt

@@ -25,6 +25,7 @@ import androidx.compose.foundation.verticalScroll
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.automirrored.rounded.ArrowBack
 import androidx.compose.material.icons.rounded.AutoAwesome
+import androidx.compose.material.icons.rounded.Language
 import androidx.compose.material.icons.rounded.Palette
 import androidx.compose.material.icons.rounded.Person
 import androidx.compose.material.icons.rounded.Settings
@@ -66,6 +67,7 @@ fun SettingsScreen(
     val appearanceMode by viewModel.appearanceMode.collectAsState()
     val userName by viewModel.userName.collectAsState()
     val userEmail by viewModel.userEmail.collectAsState()
+    val locale by viewModel.locale.collectAsState()
 
     MeshBackground {
         Column(
@@ -123,6 +125,14 @@ fun SettingsScreen(
                         }
                     }
                 }
+                Spacer(Modifier.height(12.dp))
+                SettingsOptionRow(title = stringResource(R.string.settings_language_title), description = stringResource(R.string.settings_language_desc), icon = Icons.Rounded.Language) {
+                    Row(horizontalArrangement = Arrangement.spacedBy(6.dp), verticalAlignment = Alignment.CenterVertically) {
+                        listOf("system" to R.string.settings_language_system, "de" to R.string.settings_language_de, "en" to R.string.settings_language_en).forEach { (code, labelRes) ->
+                            AppearanceTogglePill(selected = locale == code, label = stringResource(labelRes), onClick = { viewModel.selectLocale(code) })
+                        }
+                    }
+                }
             }
 
             Text(stringResource(R.string.settings_section_profile), color = cs.onSurfaceVariant.copy(alpha = 0.6f), fontSize = 12.sp, fontWeight = FontWeight.Bold, modifier = Modifier.padding(start = 8.dp, bottom = 8.dp))

app/src/main/java/dev/kaizen/app/settings/SettingsViewModel.kt

@@ -1,6 +1,7 @@
 package dev.kaizen.app.settings
 
 import androidx.lifecycle.ViewModel
+import dev.kaizen.app.net.SecureStore
 import dev.kaizen.app.ui.theme.themes.KaizenThemeId
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
@@ -8,33 +9,50 @@ import kotlinx.coroutines.flow.asStateFlow
 
 enum class AppAppearance { Light, Dark, System }
 
-class SettingsViewModel : ViewModel() {
+class SettingsViewModel(private val store: SecureStore? = null) : ViewModel() {
 
-    private val _selectedTheme = MutableStateFlow(KaizenThemeId.AMBER)
+    private val _selectedTheme = MutableStateFlow(
+        store?.loadThemeId()?.let { KaizenThemeId.fromString(it) } ?: KaizenThemeId.AMBER
+    )
     val selectedTheme: StateFlow<KaizenThemeId> = _selectedTheme.asStateFlow()
 
-    private val _appearanceMode = MutableStateFlow(AppAppearance.System)
+    private val _appearanceMode = MutableStateFlow(
+        store?.loadAppearance()?.let { runCatching { AppAppearance.valueOf(it) }.getOrNull() } ?: AppAppearance.System
+    )
     val appearanceMode: StateFlow<AppAppearance> = _appearanceMode.asStateFlow()
 
-    private val _userName = MutableStateFlow("Bruno")
+    private val _userName = MutableStateFlow(store?.loadUserName() ?: "")
     val userName: StateFlow<String> = _userName.asStateFlow()
 
     private val _userEmail = MutableStateFlow("")
     val userEmail: StateFlow<String> = _userEmail.asStateFlow()
 
+    private val _locale = MutableStateFlow(store?.loadLocale() ?: "system")
+    val locale: StateFlow<String> = _locale.asStateFlow()
+
     fun selectTheme(themeId: KaizenThemeId) {
         _selectedTheme.value = themeId
+        store?.saveThemeId(themeId.value)
     }
 
     fun selectAppearance(mode: AppAppearance) {
         _appearanceMode.value = mode
+        store?.saveAppearance(mode.name)
     }
 
     fun updateUserName(name: String) {
-        if (name.isNotBlank()) _userName.value = name.trim()
+        if (name.isNotBlank()) {
+            _userName.value = name.trim()
+            store?.saveUserName(name.trim())
+        }
     }
 
     fun updateUserEmail(email: String) {
         _userEmail.value = email
     }
+
+    fun selectLocale(locale: String) {
+        _locale.value = locale
+        store?.saveLocale(locale)
+    }
 }

app/src/main/res/values-en/strings.xml

@@ -91,4 +91,9 @@
     <string name="settings_appearance_light">Light</string>
     <string name="settings_appearance_dark">Dark</string>
     <string name="settings_appearance_system">System</string>
+    <string name="settings_language_title">Language</string>
+    <string name="settings_language_desc">Choose the app language</string>
+    <string name="settings_language_system">System</string>
+    <string name="settings_language_de">Deutsch</string>
+    <string name="settings_language_en">English</string>
 </resources>

app/src/main/res/values/strings.xml

@@ -93,4 +93,9 @@
     <string name="settings_appearance_light">Hell</string>
     <string name="settings_appearance_dark">Dunkel</string>
     <string name="settings_appearance_system">System</string>
+    <string name="settings_language_title">Sprache</string>
+    <string name="settings_language_desc">Wähle die App-Sprache</string>
+    <string name="settings_language_system">System</string>
+    <string name="settings_language_de">Deutsch</string>
+    <string name="settings_language_en">English</string>
 </resources>

app/src/test/java/dev/kaizen/app/SettingsViewModelTest.kt

@@ -13,7 +13,7 @@ class SettingsViewModelTest {
         val viewModel = SettingsViewModel()
         assertEquals(KaizenThemeId.AMBER, viewModel.selectedTheme.value)
         assertEquals(AppAppearance.System, viewModel.appearanceMode.value)
-        assertEquals("Bruno", viewModel.userName.value)
+        assertEquals("", viewModel.userName.value)
     }
 
     @Test
@@ -49,6 +49,7 @@ class SettingsViewModelTest {
     @Test
     fun testUpdateUserNameBlankIgnored() {
         val viewModel = SettingsViewModel()
+        viewModel.updateUserName("Bruno")
         viewModel.updateUserName("   ")
         assertEquals("Bruno", viewModel.userName.value)
     }