Pdf text reflow (#36)

* Implemented PDF reflow mode by introducing a mechanism to convert PDF content to Markdown/HTML for viewing in the EPUB reader.

Specific changes include:
- Added `PdfReflowGenerator` and `PdfToMarkdownGenerator` to handle PDF text extraction and conversion to reflowable formats.
- Updated `MainViewModel` with `toggleReflowMode` logic to switch between original PDF and reflowed views.
- Modified `RecentFileEntity` and `RecentFileDao` to persist user reflow preferences, including a Room database migration (v12 to v13).
- Updated `PdfViewerScreen` and `EpubReaderControls` to include UI options for toggling reflow mode.
- Integrated reflow preference check into the book opening workflow to automatically load the preferred view.
- Updated `AppNavigation` and `EpubReaderScreen` to support the new view switching state.

* Implemented background processing and incremental loading for PDF reflow mode.

- Added `reflowProgress` to `MainViewModel` to track and display PDF-to-Markdown conversion progress in the UI.
- Refactored `PdfToMarkdownGenerator` to generate a skeleton EPUB structure immediately while processing page content (text and images) asynchronously.
- Switched PDF text extraction to use `PDFBox` with optimized memory settings and JPEG compression for images.
- Implemented priority page processing in reflow mode, starting with the user's current page.
- Added "Clear Reflow Cache" debug option to the Home Screen.
- Enhanced `BookPaginator` to support lazy loading of chapter content from disk and improved cache hit detection.

* Refactored PDF Reflow Mode to generate standalone Markdown files instead of temporary EPUB books.

* perf(reflow): optimize PDF-to-Markdown conversion and fix viewing lag

- Re-architected PdfToMarkdownGenerator to use a single-pass stream (O(N) complexity), fixing performance bottlenecks and timeouts on large PDFs.
- Implemented "Virtual Chaptering" in SingleFileImporter for Markdown files to split content into page-level HTML files, eliminating UI lag during reading.
- Simplified ReflowWorker to delegate progress tracking and looping to the generator.
- Enhanced PdfViewerScreen with a prominent top-bar progress indicator and a completion snackbar with an "OPEN" action.

* Optimized EPUB parsing performance and fixed PDF viewer UI layout.

- Optimized `EpubParser` by implementing parallel chapter parsing using coroutines and a semaphore to limit concurrency.
- Reduced memory usage in `EpubParser` and `SingleFileImporter` by no longer storing full HTML content in memory for chapters.
- Updated `EpubXMLFileParser` to support an existing `Document` object to avoid redundant Jsoup parsing.
- Fixed an issue in `PdfViewerScreen` where the snackbar was appearing under the bottom app bar.

app/src/main/java/com/aryan/reader/paginatedreader/PaginatedReader.kt

@@ -655,7 +655,10 @@ fun PaginatedReaderScreen(
                 BookCacheDatabase.getDatabase(context.applicationContext).bookCacheDao()
             val proto = ProtoBuf { serializersModule = semanticBlockModule }
 
-            Timber.d("Recreating BookPaginator. TextAlign: $userTextAlign")
+            val uniqueBookId = if (book.fileName.length > 20) book.fileName else book.title
+
+            Timber.d("Recreating BookPaginator for ID: $uniqueBookId. TextAlign: $userTextAlign")
+            Timber.tag("ReflowPaginationDiag").d("PaginatedReaderScreen: Instantiating BookPaginator. book.chaptersForPagination.size=${book.chaptersForPagination.size}, initialChapter=$effectiveInitialChapter")
 
             BookPaginator(
                 coroutineScope = coroutineScope,
@@ -667,7 +670,7 @@ fun PaginatedReaderScreen(
                 density = density,
                 fontFamilyMap = fontFamilyMap,
                 isDarkTheme = isDarkTheme,
-                bookId = book.title,
+                bookId = uniqueBookId,
                 bookCacheDao = bookCacheDao,
                 proto = proto,
                 initialChapterToPaginate = effectiveInitialChapter,
@@ -719,23 +722,29 @@ fun PaginatedReaderScreen(
             }
         }
 
-        // FIX 2: Replace property delegates with local state and a LaunchedEffect observer.
         var isLoading by remember { mutableStateOf(true) }
         var totalPageCount by remember { mutableIntStateOf(0) }
         var generation by remember { mutableIntStateOf(0) }
 
         LaunchedEffect(paginator) {
-            launch { snapshotFlow { paginator.isLoading }.collect { isLoading = it } }
+            launch { snapshotFlow { paginator.isLoading }.collect {
+                Timber.tag("ReflowPaginationDiag").d("PaginatedReaderScreen: paginator.isLoading=$it")
+                isLoading = it
+            } }
             launch {
                 snapshotFlow { paginator.totalPageCount }.collect { newTotalPageCount ->
+                    Timber.tag("ReflowPaginationDiag").d("PaginatedReaderScreen: paginator.totalPageCount=$newTotalPageCount")
                     totalPageCount = newTotalPageCount
                 }
             }
-            launch { snapshotFlow { paginator.generation }.collect { generation = it } }
+            launch { snapshotFlow { paginator.generation }.collect {
+                Timber.tag("ReflowPaginationDiag").d("PaginatedReaderScreen: paginator.generation=$it")
+                generation = it
+            } }
         }
 
         LaunchedEffect(pagerState, paginator) {
-            snapshotFlow { pagerState.currentPage }.debounce(500) // Wait for scrolling to settle
+            snapshotFlow { pagerState.currentPage }.debounce(500)
                 .collectLatest { page -> paginator.onUserScrolledTo(page) }
         }
 
@@ -1432,6 +1441,7 @@ internal fun PaginatedReaderContent(
             CircularProgressIndicator()
         }
     } else {
+        Timber.tag("ReflowPaginationDiag").d("PaginatedReaderContent: isLoading=false, totalPageCount=${uiState.totalPageCount}")
         if (uiState.totalPageCount > 0) {
             uiState.generation
 
@@ -1508,7 +1518,9 @@ internal fun PaginatedReaderContent(
                     var currentChapterPath by remember { mutableStateOf<String?>(null) }
 
                     LaunchedEffect(pageIndex, uiState.generation) {
+                        Timber.tag("ReflowPaginationDiag").d("PaginatedReaderContent: Fetching page $pageIndex content. generation=${uiState.generation}")
                         pageContent = onGetPage(pageIndex)
+                        Timber.tag("ReflowPaginationDiag").d("PaginatedReaderContent: Fetched page $pageIndex content. isNull=${pageContent == null}, blocks=${pageContent?.content?.size}")
                         onGetChapterPath(pageIndex)?.let { currentChapterPath = it }
                     }