feat: Enhance chat UI with group invite handling and new download indicator

- Added support for standalone group invites in MessageBubble component.
- Improved bubble padding and width handling for group invites.
- Refactored MessageBubble to streamline background and border logic.
- Introduced AnimatedDownloadIndicator for a more engaging download experience.
- Created ThemeWallpapers data structure to manage chat wallpapers.
- Implemented WallpaperSelectorRow and WallpaperSelectorItem for theme customization.
- Updated ThemeScreen to allow wallpaper selection and preview.
- Added new drawable resources for download and search icons.

app/src/main/java/com/rosetta/messenger/data/PreferencesManager.kt

@@ -27,6 +27,7 @@ class PreferencesManager(private val context: Context) {
         val HAS_SEEN_ONBOARDING = booleanPreferencesKey("has_seen_onboarding")
         val IS_DARK_THEME = booleanPreferencesKey("is_dark_theme")
         val THEME_MODE = stringPreferencesKey("theme_mode") // "light", "dark", "auto"
+        val CHAT_WALLPAPER_ID = stringPreferencesKey("chat_wallpaper_id") // empty = no wallpaper
 
         // Notifications
         val NOTIFICATIONS_ENABLED = booleanPreferencesKey("notifications_enabled")
@@ -100,6 +101,13 @@ class PreferencesManager(private val context: Context) {
         context.dataStore.edit { preferences -> preferences[THEME_MODE] = value } // Persist
     }
 
+    val chatWallpaperId: Flow<String> =
+            context.dataStore.data.map { preferences -> preferences[CHAT_WALLPAPER_ID] ?: "" }
+
+    suspend fun setChatWallpaperId(value: String) {
+        context.dataStore.edit { preferences -> preferences[CHAT_WALLPAPER_ID] = value }
+    }
+
     // ═════════════════════════════════════════════════════════════
     // 🔔 NOTIFICATIONS
     // ═════════════════════════════════════════════════════════════