v1.0.25: multi-select files, unified notification, dark theme, icon redesign

- FilesScreen: long-press enters selection mode, bulk share/delete toolbar, BackHandler
- FilesViewModel: ShareMultiple action, isSelectionMode/selectedCount state, download-to-cache for open/share
- FileWatchService: recursive FileObserver per subdirectory; unified notification updated with sync result via WorkManager flow observation
- SyncWorker: silent flag suppresses notifications when triggered by watcher; emits KEY_RESULT_SUMMARY output data
- Passbolt-inspired dark theme (Red700/Red500 primary, near-black surface)
- App icon: circular AutoSync-style sync arrows (cyan gradient, deep navy background)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/src/main/kotlin/com/syncflow/ui/theme/Theme.kt

@@ -13,41 +13,43 @@ import androidx.compose.ui.unit.sp
 import androidx.core.view.WindowCompat
 
 private val LightColors = lightColorScheme(
-    primary            = Indigo600,
+    primary            = Red700,
     onPrimary          = Color.White,
-    primaryContainer   = Indigo100,
-    onPrimaryContainer = Indigo900,
-    secondary          = Teal600,
+    primaryContainer   = Red50,
+    onPrimaryContainer = Red900,
+    secondary          = Orange700,
     onSecondary        = Color.White,
-    secondaryContainer = Teal100,
+    secondaryContainer = Orange100,
     tertiary           = Amber500,
     tertiaryContainer  = Amber100,
-    background         = Slate50,
+    background         = Gray50,
     surface            = Color.White,
-    surfaceVariant     = Slate100,
-    onSurfaceVariant   = Slate600,
+    surfaceVariant     = Gray100,
+    onSurface          = Gray900,
+    onSurfaceVariant   = Gray600,
     error              = RedError,
-    errorContainer     = Color(0xFFFEE2E2),
-    outline            = Slate200,
+    errorContainer     = Red50,
+    outline            = Gray200,
 )
 
 private val DarkColors = darkColorScheme(
-    primary            = Color(0xFF818CF8),
-    onPrimary          = Indigo900,
-    primaryContainer   = Color(0xFF3730A3),
-    onPrimaryContainer = Indigo100,
-    secondary          = Color(0xFF2DD4BF),
-    onSecondary        = Color(0xFF003731),
-    secondaryContainer = Color(0xFF00504A),
+    primary            = Red500,
+    onPrimary          = Color.White,
+    primaryContainer   = Red900,
+    onPrimaryContainer = Red100,
+    secondary          = Color(0xFFFF7043),
+    onSecondary        = Color.White,
+    secondaryContainer = Color(0xFF4E1500),
     tertiary           = Amber500,
-    tertiaryContainer  = Color(0xFF92400E),
-    background         = Color(0xFF0F0F1A),
-    surface            = Color(0xFF1A1A2E),
-    surfaceVariant     = Color(0xFF252538),
-    onSurfaceVariant   = Color(0xFF94A3B8),
-    error              = Color(0xFFF87171),
-    errorContainer     = Color(0xFF7F1D1D),
-    outline            = Color(0xFF334155),
+    tertiaryContainer  = Color(0xFF3E2700),
+    background         = Color(0xFF0F0F0F),
+    surface            = Color(0xFF1C1C1C),
+    surfaceVariant     = Color(0xFF2A2A2A),
+    onSurface          = Color(0xFFEAEAEA),
+    onSurfaceVariant   = Color(0xFF9E9E9E),
+    error              = Color(0xFFFF5252),
+    errorContainer     = Color(0xFF5C0000),
+    outline            = Color(0xFF3D3D3D),
 )
 
 private val AppTypography = Typography(