Folder pdf annotation sync (#32)

* Implemented folder-based annotation synchronization and legacy book ID migration.

- Added `syncLocalAnnotationsToFolder` and `importAnnotationBundle` to `RecentFilesRepository` to handle bundling ink, rich text, layouts, and text boxes into a single JSON sidecar file.
- Introduced `saveAnnotationSidecar` and `getAnnotationSidecar` in `LocalSyncUtils` to manage hidden synchronization files in linked folders using SAF.
- Updated `MainViewModel` to trigger annotation syncing on book close and added a migration utility for legacy book IDs.
- Enhanced `FolderSyncWorker` to include a dedicated phase for importing newer annotation bundles from synchronized folders.
- Fixed an ID mismatch edge case in `PdfViewerScreen` by initiating data migration when a legacy ID is detected.
- Added `selectedBookId` to `ReaderScreenState` to better track the active document across the application.

* fix(sync): resolve Syncthing file lock conflicts and annotation migration bug

- Implement atomic saves (write-to-temp then rename) for annotation sidecars in `LocalSyncUtils` to prevent `.tmp` file locking and partial writes when using third-party sync tools like Syncthing.
- Add robust conflict resolution for annotation sidecars (`resolveAndCleanAnnotationConflicts`) to automatically detect, keep the newest version, and clean up `.sync-conflict` files.
- Fix a bug in `MainViewModel.checkAndMigrateLegacyBookId` where older legacy local files would blindly overwrite newly synced annotation files by adding a timestamp-based clobber check.

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

@@ -2255,7 +2255,15 @@ fun PdfViewerScreen(
         flatTableOfContents = emptyList()
 
         val fastId = getFastFileId(context, pdfUri)
-        currentBookId = fastId
+        val selectedId = uiState.selectedBookId
+
+        if (selectedId != null && selectedId != fastId) {
+            Timber.tag("FolderAnnotationSync").i("Detected ID mismatch. Legacy: $fastId, Selected: $selectedId. Initiating migration.")
+            viewModel.checkAndMigrateLegacyBookId(fastId, selectedId)
+            currentBookId = selectedId
+        } else {
+            currentBookId = fastId
+        }
 
         val oldDoc = pdfDocument
         val oldPfd = pfdState