Expanded folder sync functionality to support multiple folders and improved performance. (#47)

- Added `SyncedFolder` data class and transitioned from a single `syncedFolderUri` to a list of `syncedFolders`.
- Implemented logic to add, remove, and persist multiple synced folders using JSON in shared preferences, including a migration path for legacy single-folder settings.
- Updated `FolderSyncWorker` to iterate through all registered folders and added an annotation sidecar preloading optimization to reduce file I/O during sync.
- Redesigned the "Folder Sync" UI in `LibraryScreen` to display a list of active folders with individual management options and a 3-folder limit.
- Refined permission handling to request both read and write access for synced folders.

app/src/main/java/com/aryan/reader/MetadataExtractionWorker.kt

@@ -29,8 +29,12 @@ class MetadataExtractionWorker(
 
     override suspend fun doWork(): Result = withContext(Dispatchers.IO) {
         val prefs = appContext.getSharedPreferences("reader_user_prefs", Context.MODE_PRIVATE)
-        if (!prefs.contains(MainViewModel.KEY_SYNCED_FOLDER_URI)) {
-            Timber.tag("MetadataWorker").w("Folder disconnected. Stopping extraction worker.")
+
+        val hasLegacy = prefs.contains("synced_folder_uri")
+        val hasNew = prefs.contains("synced_folders_list_json")
+
+        if (!hasLegacy && !hasNew) {
+            Timber.tag("MetadataWorker").w("No folders linked. Stopping.")
             return@withContext Result.success()
         }
 
@@ -46,7 +50,7 @@ class MetadataExtractionWorker(
             filesToProcess.forEach { item ->
                 if (isStopped) return@forEach
 
-                if (!prefs.contains(MainViewModel.KEY_SYNCED_FOLDER_URI)) return@forEach
+                if (item.sourceFolderUri == null) return@forEach
 
                 try {
                     val uri = item.uriString?.toUri() ?: return@forEach