fix scroll buttons + restyle sidebar context menu

Scroll buttons: only one shown at a time based on direction
(up when scrolled down, down when scrolled up), hidden during
streaming. Mutually exclusive instead of both visible.

Sidebar menu: replaced default Material3 DropdownMenu/MenuItem
with custom styled menu — dark surface color (1A2030 dark,
F8F9FB light), KaizenShapes.md rounded corners, 12dp shadow
elevation, custom MenuRow composable with proper spacing.

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

@@ -569,27 +569,24 @@ fun ChatScreen(
                                 }
                             }
 
-                            // Scroll buttons
+                            if (!isStreaming) {
-                            val showScrollUp by remember { derivedStateOf { listState.firstVisibleItemIndex > 2 } }
+                                val atTop by remember { derivedStateOf { listState.firstVisibleItemIndex <= 1 } }
-                            val showScrollDown by remember { derivedStateOf {
+                                val atBottom by remember { derivedStateOf {
                                     val info = listState.layoutInfo
-                                info.visibleItemsInfo.lastOrNull()?.index != info.totalItemsCount - 1
+                                    info.visibleItemsInfo.lastOrNull()?.index == info.totalItemsCount - 1
                                 }}
+                                val canScrollUp by remember { derivedStateOf { listState.canScrollBackward } }
+                                val canScrollDown by remember { derivedStateOf { listState.canScrollForward } }
 
-                            if (showScrollUp || showScrollDown) {
+                                if (!atTop && canScrollUp) {
-                                Column(
-                                    modifier = Modifier
-                                        .align(Alignment.CenterEnd)
-                                        .padding(end = 8.dp),
-                                    verticalArrangement = Arrangement.spacedBy(8.dp),
-                                ) {
-                                    if (showScrollUp) {
                                     GlassSurface(
                                         shape = KaizenShapes.circle,
                                         tintAlpha = GlassTiers.pill(isSystemInDarkTheme()),
                                         shadowStack = KaizenShadows.level1,
                                         cornerRadius = 18.dp,
                                         modifier = Modifier
+                                            .align(Alignment.CenterEnd)
+                                            .padding(end = 8.dp, bottom = 24.dp)
                                             .size(36.dp)
                                             .clickable { scope.launch { listState.animateScrollToItem(0) } },
                                     ) {
@@ -597,14 +594,15 @@ fun ChatScreen(
                                             Icon(Icons.Rounded.KeyboardArrowUp, null, tint = MaterialTheme.colorScheme.onBackground, modifier = Modifier.size(20.dp))
                                         }
                                     }
-                                    }
+                                } else if (!atBottom && canScrollDown) {
-                                    if (showScrollDown) {
                                     GlassSurface(
                                         shape = KaizenShapes.circle,
                                         tintAlpha = GlassTiers.pill(isSystemInDarkTheme()),
                                         shadowStack = KaizenShadows.level1,
                                         cornerRadius = 18.dp,
                                         modifier = Modifier
+                                            .align(Alignment.CenterEnd)
+                                            .padding(end = 8.dp, top = 24.dp)
                                             .size(36.dp)
                                             .clickable { scope.launch { listState.animateScrollToItem(messages.size - 1) } },
                                     ) {
@@ -615,7 +613,6 @@ fun ChatScreen(
                                 }
                             }
                         }
-                        }
 
                         // 2. Floating Top Menu Button
                         val scrimColor = MaterialTheme.colorScheme.background

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

@@ -34,8 +34,7 @@ import androidx.compose.material.icons.rounded.Search
 import androidx.compose.material.icons.rounded.Settings
 import androidx.compose.material.icons.rounded.Star
 import androidx.compose.material3.AlertDialog
-import androidx.compose.material3.DropdownMenu
+import androidx.compose.ui.graphics.vector.ImageVector
-import androidx.compose.material3.DropdownMenuItem
 import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
@@ -423,48 +422,38 @@ private fun HistoryItemRow(
             }
         }
 
-        DropdownMenu(
+        androidx.compose.material3.DropdownMenu(
             expanded = showMenu,
             onDismissRequest = { showMenu = false },
+            containerColor = if (isDark) Color(0xFF1A2030) else Color(0xFFF8F9FB),
+            shadowElevation = 12.dp,
+            shape = KaizenShapes.md,
         ) {
             if (!item.locked) {
-                DropdownMenuItem(
+                MenuRow(Icons.Rounded.Edit, stringResource(R.string.sidebar_rename), cs.onBackground) { showMenu = false; onRename() }
-                    text = { Text(stringResource(R.string.sidebar_rename), fontSize = 14.sp) },
-                    onClick = { showMenu = false; onRename() },
-                    leadingIcon = { Icon(Icons.Rounded.Edit, null, modifier = Modifier.size(18.dp)) },
-                )
             }
-            DropdownMenuItem(
+            MenuRow(Icons.Rounded.PushPin, stringResource(if (item.pinned) R.string.sidebar_unpin else R.string.sidebar_pin), cs.onBackground) { showMenu = false; onTogglePin() }
-                text = {
+            MenuRow(
-                    Text(
-                        stringResource(if (item.pinned) R.string.sidebar_unpin else R.string.sidebar_pin),
-                        fontSize = 14.sp,
-                    )
-                },
-                onClick = { showMenu = false; onTogglePin() },
-                leadingIcon = { Icon(Icons.Rounded.PushPin, null, modifier = Modifier.size(18.dp)) },
-            )
-            DropdownMenuItem(
-                text = {
-                    Text(
-                        stringResource(if (item.locked) R.string.sidebar_unlock else R.string.sidebar_lock),
-                        fontSize = 14.sp,
-                    )
-                },
-                onClick = { showMenu = false; onToggleLock() },
-                leadingIcon = {
-                    Icon(
                 if (item.locked) Icons.Rounded.LockOpen else Icons.Rounded.Lock,
-                        null,
+                stringResource(if (item.locked) R.string.sidebar_unlock else R.string.sidebar_lock),
-                        modifier = Modifier.size(18.dp),
+                cs.onBackground,
-                    )
+            ) { showMenu = false; onToggleLock() }
-                },
+            MenuRow(Icons.Rounded.Delete, stringResource(R.string.sidebar_delete), Color(0xFFEF4444)) { showMenu = false; onDelete() }
-            )
-            DropdownMenuItem(
-                text = { Text(stringResource(R.string.sidebar_delete), fontSize = 14.sp, color = Color(0xFFEF4444)) },
-                onClick = { showMenu = false; onDelete() },
-                leadingIcon = { Icon(Icons.Rounded.Delete, null, tint = Color(0xFFEF4444), modifier = Modifier.size(18.dp)) },
-            )
         }
     }
 }
+
+@Composable
+private fun MenuRow(icon: ImageVector, label: String, tint: Color, onClick: () -> Unit) {
+    Row(
+        modifier = Modifier
+            .fillMaxWidth()
+            .clickable(onClick = onClick)
+            .padding(horizontal = 16.dp, vertical = 12.dp),
+        verticalAlignment = Alignment.CenterVertically,
+    ) {
+        Icon(icon, null, tint = tint.copy(alpha = 0.7f), modifier = Modifier.size(18.dp))
+        Spacer(Modifier.width(12.dp))
+        Text(label, color = tint, fontSize = 14.sp, fontWeight = FontWeight.Medium)
+    }
+}