Folder import\sync rework (#18)

* feat: rework Folder Sync architecture to separate Managed vs Linked books

- Introduced "Managed" (imported to app storage) vs "Linked" (SAF URI) book logic.
- Disabled Google Drive/Metadata synchronization for Folder-Linked books to respect privacy and storage.
- Updated deletion logic: Folder books are now marked as deleted in the DB to blacklist them from future auto-scans, while Managed books are permanently purged from local and cloud storage.
- Enhanced folder sync discoverability by adding a direct "Sync Folder" navigation button in Home screen.
- Implemented reactive pager navigation in MainScreen and LibraryScreen via LaunchedEffect to allow programmatic tab switching from the ViewModel.

* Implemented a local folder synchronization system to track and update book metadata across devices.

Key changes:
- Added `FolderBookMetadata` and `LocalSyncUtils` for serializing and managing metadata files in a `.episteme` directory.
- Implemented bidirectional sync in `FolderSyncWorker` to reconcile local database state with folder-based metadata using timestamps and Syncthing conflict resolution.
- Updated `MainViewModel` to trigger folder metadata sync when closing a book and verify for remote updates upon opening.
- Enhanced folder management with manual scan support via `WorkManager` and automatic cleanup of database entries when a folder is disconnected.
- Added `RecentFileDao` methods to support bulk deletion and prefix-based file lookups.

* Removed API 34 restriction for chapter processing and updated local folder sync directory name

* Increased TTS timeouts, added edge-to-edge support in MainScreen, and improved TtsChunk mapping safety

* Improved folder synchronization and metadata management.

- Added metadata-only sync option and triggered it on app start.
- Implemented hidden metadata filenames (prefixed with `.`) to reduce file clutter.
- Added automatic creation of `.nomedia` files in the sync directory.
- Enhanced sync conflict resolution by picking the latest metadata and cleaning up obsolete or orphaned files.
- Added "Sync Metadata" button to the Library screen.
- Updated UI labels for local folder sync to clarify Google Drive integration.
- Refactored `FolderSyncWorker` to support targeted metadata-only synchronization.

* Implement folder sync migration and refactoring

- Added a migration dialog to inform users about the folder sync refactor, where books are now read directly from external storage.
- Updated `MainViewModel` to handle migration state and trigger a full scan upon completion or dismissal of the dialog.
- Modified `FolderSyncWorker` to support legacy book matching during migration, updating file URIs and cleaning up internal app storage for migrated books.
- Improved synchronization logic between local and remote metadata, including cleanup of orphaned metadata files.
- Refined `RecentFileItem` updates during sync to preserve progress and bookmarks based on last modified timestamps.

* Implemented pull-to-refresh for library sync and enhanced folder file deletion.

- Added `isRefreshing` state to `MainViewModel` and integrated `PullToRefreshBox` in `HomeScreen`.
- Implemented `refreshLibrary` to trigger cloud and folder metadata synchronization.
- Updated deletion logic to physically remove files and metadata from synced local folders.
- Added a warning to the delete confirmation dialog when removing folder-synced items.
- Improved folder sync reliability by performing lazy cleanup of missing files during interaction and sync.
- Fixed a bug where sync loading indicators would not retract on failure or cancellation.

* Improved bookmark navigation and scroll synchronization in EPUB reader

- Refined bookmark navigation logic for vertical scroll mode to handle chunk injection more reliably.
- Added `isNavigatingToBookmark` state to show a loading overlay during long jumps.
- Implemented `onScrollFinished` callback in `CfiJsBridge` to synchronize UI state with WebView scroll completion.
- Updated `ChapterWebView` to use `rememberUpdatedState` for JavaScript bridge callbacks to ensure data consistency.
- Improved `getCurrentCfi` and `scrollToCfi` in `epub_reader.js` with better visibility probing and retry logic for detached nodes.

* Implemented background metadata extraction for folder sync.

Key changes:
- Added `MetadataExtractionWorker` to handle heavy metadata and cover extraction for files in the background.
- Refactored `FolderSyncWorker` to perform fast file discovery using placeholders, enqueuing the metadata worker upon completion.
- Added `getFolderBooksWithoutCovers` query to `RecentFileDao`.
- Updated UI components (`EmptyState`, `MainViewModel`) to improve user feedback during sync and provide clear setup actions.
- Enhanced `EmptyState` composable to support secondary actions and custom button text.

* Updated Library Screen UI

app/src/main/java/com/aryan/reader/pdf/PdfViewerScreen.kt

@@ -565,8 +565,6 @@ fun PdfViewerScreen(
     initialPage: Int?,
     initialBookmarksJson: String?,
     isProUser: Boolean,
-    pendingSyncUpdate: SyncUpdateInfo?,
-    onClearPendingSyncUpdate: () -> Unit,
     onNavigateBack: () -> Unit,
     onSavePosition: (page: Int, totalPages: Int) -> Unit,
     onBookmarksChanged: (bookmarksJson: String) -> Unit,
@@ -1553,39 +1551,6 @@ fun PdfViewerScreen(
 
     var showRenameBookmarkDialog by remember { mutableStateOf<PdfBookmark?>(null) }
 
-    LaunchedEffect(pendingSyncUpdate) {
-        if (pendingSyncUpdate != null) {
-            val newPage = pendingSyncUpdate.page
-            val message = if (newPage != null) {
-                "Newer reading position found. Sync to page ${newPage + 1}?"
-            } else {
-                "Bookmarks updated on another device. Sync now?"
-            }
-
-            val result = withTimeoutOrNull(10_000L) {
-                snackbarHostState.showSnackbar(
-                    message = message,
-                    actionLabel = "Sync",
-                    withDismissAction = true,
-                    duration = SnackbarDuration.Indefinite
-                )
-            }
-
-            if (result == SnackbarResult.ActionPerformed) {
-                if (newPage != null) {
-                    when (displayMode) {
-                        DisplayMode.PAGINATION -> pagerState.scrollToPage(newPage)
-                        DisplayMode.VERTICAL_SCROLL -> verticalReaderState.scrollToPage(newPage)
-                    }
-                }
-                pendingSyncUpdate.bookmarksJson?.let { newBookmarksJson ->
-                    bookmarks = loadPdfBookmarksFromJson(newBookmarksJson)
-                }
-            }
-            onClearPendingSyncUpdate()
-        }
-    }
-
     var isOcrModelDownloading by remember { mutableStateOf(false) }
 
     LaunchedEffect(isOcrModelDownloading) {