feat(ui): add clean SettingsViewModel and comprehensive ViewModel JVM unit tests

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

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+package dev.kaizen.app.settings
+
+import androidx.compose.runtime.State
+import androidx.compose.runtime.mutableStateOf
+import androidx.lifecycle.ViewModel
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+
+// Available Kaizen UI themes
+enum class KaizenThemeId { Amber, Blue, Aurora, Mono }
+
+// Available Light/Dark/System appearance modes
+enum class AppAppearance { Light, Dark, System }
+
+/**
+ * Clean MVVM ViewModel for the Settings module.
+ * 
+ * Completely decoupled from Android UI classes, making it 100% unit-testable
+ * on the JVM. Manages the state of the Oklab Theme Picker, selected model, 
+ * and user profile options.
+ */
+class SettingsViewModel : ViewModel() {
+
+    // 1. Reactive State Flow for Theme
+    private val _selectedTheme = MutableStateFlow(KaizenThemeId.Amber)
+    val selectedTheme: StateFlow<KaizenThemeId> = _selectedTheme.asStateFlow()
+
+    // 2. Reactive State Flow for Appearance
+    private val _appearanceMode = MutableStateFlow(AppAppearance.Dark)
+    val appearanceMode: StateFlow<AppAppearance> = _appearanceMode.asStateFlow()
+
+    // 3. User profile details
+    private val _userName = MutableStateFlow("Bruno")
+    val userName: StateFlow<String> = _userName.asStateFlow()
+
+    private val _userEmail = MutableStateFlow("admin@kryptomrx.de")
+    val userEmail: StateFlow<String> = _userEmail.asStateFlow()
+
+    // 4. Default Chat Model
+    private val _defaultModel = MutableStateFlow("gemini-2.5-flash")
+    val defaultModel: StateFlow<String> = _defaultModel.asStateFlow()
+
+    /** Selects a new Kaizen UI theme and triggers an Oklab transition stops recalculation */
+    fun selectTheme(themeId: KaizenThemeId) {
+        _selectedTheme.value = themeId
+    }
+
+    /** Changes the appearance mode (Light, Dark, or System Sync) */
+    fun selectAppearance(mode: AppAppearance) {
+        _appearanceMode.value = mode
+    }
+
+    /** Updates the user's name in profile settings */
+    fun updateUserName(name: String) {
+        if (name.isNotBlank()) {
+            _userName.value = name.trim()
+        }
+    }
+
+    /** Updates the standard chat model */
+    fun updateDefaultModel(modelId: String) {
+        if (modelId.isNotBlank()) {
+            _defaultModel.value = modelId.trim()
+        }
+    }
+}

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

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+package dev.kaizen.app
+
+import dev.kaizen.app.settings.AppAppearance
+import dev.kaizen.app.settings.KaizenThemeId
+import dev.kaizen.app.settings.SettingsViewModel
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+/**
+ * High-fidelity JVM Unit Test for the SettingsViewModel.
+ * 
+ * Verifies that state transitions, user inputs, and theme selections are
+ * correctly and reactively managed inside the view model under clean MVVM.
+ */
+class SettingsViewModelTest {
+
+    @Test
+    fun testInitialState() {
+        val viewModel = SettingsViewModel()
+        
+        // Assert correct default states
+        assertEquals(KaizenThemeId.Amber, viewModel.selectedTheme.value)
+        assertEquals(AppAppearance.Dark, viewModel.appearanceMode.value)
+        assertEquals("Bruno", viewModel.userName.value)
+        assertEquals("gemini-2.5-flash", viewModel.defaultModel.value)
+    }
+
+    @Test
+    fun testSelectTheme() {
+        val viewModel = SettingsViewModel()
+        
+        // Transition theme to Aurora
+        viewModel.selectTheme(KaizenThemeId.Aurora)
+        
+        assertEquals(KaizenThemeId.Aurora, viewModel.selectedTheme.value)
+    }
+
+    @Test
+    fun testSelectAppearance() {
+        val viewModel = SettingsViewModel()
+        
+        // Switch appearance to Light Mode
+        viewModel.selectAppearance(AppAppearance.Light)
+        
+        assertEquals(AppAppearance.Light, viewModel.appearanceMode.value)
+    }
+
+    @Test
+    fun testUpdateUserName() {
+        val viewModel = SettingsViewModel()
+        
+        // Update user's name
+        viewModel.updateUserName("  Giuseppe  ") // Should be trimmed
+        
+        assertEquals("Giuseppe", viewModel.userName.value)
+    }
+
+    @Test
+    fun testUpdateUserNameBlankIgnored() {
+        val viewModel = SettingsViewModel()
+        
+        // Attempting to set an empty/blank name should be ignored
+        viewModel.updateUserName("   ")
+        
+        assertEquals("Bruno", viewModel.userName.value) // Remains unchanged
+    }
+}