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/SharedComposables.kt

@@ -86,6 +86,7 @@ import androidx.browser.customtabs.CustomTabsIntent
 import androidx.compose.foundation.clickable
 import androidx.compose.material.icons.filled.SelectAll
 import androidx.compose.material3.HorizontalDivider
+import androidx.compose.material3.OutlinedButton
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.setValue
@@ -261,20 +262,43 @@ fun CustomTopAppBar(
 }
 
 @Composable
-fun DeleteConfirmationDialog(count: Int, onConfirm: () -> Unit, onDismiss: () -> Unit, isPermanentDelete: Boolean = false) {
+fun DeleteConfirmationDialog(
+    count: Int,
+    onConfirm: () -> Unit,
+    onDismiss: () -> Unit,
+    isPermanentDelete: Boolean = false,
+    containsFolderItems: Boolean = false // New parameter
+) {
     val title = if (isPermanentDelete) "Delete File(s) Permanently" else "Remove from Recents"
+
     val text = if (isPermanentDelete) {
-        "Do you want to permanently delete $count selected file(s) from your device? This action cannot be undone."
+        if (containsFolderItems) {
+            "Warning: Some selected items are synced from a local folder. Proceeding will delete the actual files from your device storage.\n\nThis action cannot be undone."
+        } else {
+            "Do you want to permanently delete $count selected file(s) from your device? This action cannot be undone."
+        }
     } else {
         "Do you want to remove $count selected file(s) from the recent files list? It will reappear if you open it again from the library."
     }
+
     val confirmText = if (isPermanentDelete) "Delete" else "Remove"
+
     AlertDialog(
         onDismissRequest = onDismiss,
         title = { Text(title) },
-        text = { Text(text) },
+        text = {
+            Text(
+                text,
+                color = if (containsFolderItems && isPermanentDelete) MaterialTheme.colorScheme.error else MaterialTheme.colorScheme.onSurfaceVariant
+            )
+        },
         confirmButton = {
-            TextButton(onClick = onConfirm) { Text(confirmText) }
+            TextButton(
+                onClick = onConfirm,
+                colors = if (containsFolderItems && isPermanentDelete) ButtonDefaults.textButtonColors(contentColor = MaterialTheme.colorScheme.error) else ButtonDefaults.textButtonColors()
+            ) {
+                Text(confirmText)
+            }
         },
         dismissButton = {
             TextButton(onClick = onDismiss) { Text("Cancel") }
@@ -430,7 +454,10 @@ fun EmptyState(
     title: String,
     message: String,
     onSelectFileClick: () -> Unit,
-    modifier: Modifier = Modifier
+    modifier: Modifier = Modifier,
+    primaryButtonText: String = "Select a File",
+    secondaryButtonText: String? = null,
+    onSecondaryClick: (() -> Unit)? = null
 ) {
     Column(
         modifier = modifier
@@ -449,7 +476,8 @@ fun EmptyState(
         Text(
             text = title,
             style = MaterialTheme.typography.headlineSmall,
-            color = MaterialTheme.colorScheme.onSurface
+            color = MaterialTheme.colorScheme.onSurface,
+            textAlign = TextAlign.Center
         )
         Spacer(modifier = Modifier.height(8.dp))
         Text(
@@ -459,7 +487,15 @@ fun EmptyState(
             color = MaterialTheme.colorScheme.onSurfaceVariant
         )
         Spacer(modifier = Modifier.height(32.dp))
-        SelectFileButton(onClick = onSelectFileClick, text = "Select a File")
+
+        SelectFileButton(onClick = onSelectFileClick, text = primaryButtonText)
+
+        if (secondaryButtonText != null && onSecondaryClick != null) {
+            Spacer(modifier = Modifier.height(16.dp))
+            OutlinedButton(onClick = onSecondaryClick) {
+                Text(secondaryButtonText)
+            }
+        }
     }
 }