Pdf reflow upgrade (#63)

* Replaced PDF-to-Markdown reflow with an enhanced PDF-to-HTML generator.

Specific changes include:
- Replaced `PdfToMarkdownGenerator` and `PdfReflowGenerator` with `PdfToHtmlGenerator`.
- Added native bridge methods in `NativePdfiumBridge.kt` and `pdfium_bridge.cpp` to extract character bounding boxes, page objects, and image pixels.
- Implemented vertical merging of text and images in `PdfToHtmlGenerator` to maintain document layout.
- Added logic to detect and filter repeating headers and footers across PDF pages.
- Updated `ReflowWorker` to generate `.html` files instead of `.md` files and updated `FileType` handling.
- Simplified `SingleFileImporter` by removing dependencies on the legacy Markdown generator.

* Updated PDF to HTML generation to include page breaks and split HTML files into individual chapters based on page markers.

* Added junk character filtering and normalization to PDF text extraction

* - Added `allRecentFiles` to `ReaderScreenState` to track all files, including reflowed versions.
- Updated `recentFiles` in `MainViewModel` to filter out reflowed files (`_reflow`) from the main library view.
- Implemented `deleteBookPermanently` in `MainViewModel` to handle book deletion and cache cleanup.
- Added a "Delete Text View" option to the `EpubReader` controls for reflowed files.
- Improved reflow file detection in `PdfViewerScreen` by checking against `allRecentFiles`.

* Implemented a centralized data-saving mechanism in `PdfViewerScreen` using a debounced `saveAllData` function. This refactor consolidates the saving of annotations, text boxes, highlights, bookmarks, and scroll positions, adding lifecycle-aware triggers and a mutex to ensure data integrity during pauses or document navigation.

* Optimized PDF selection and annotation performance by offloading heavy operations to background threads and improving UI responsiveness.

- Moved PDF page/text opening, character range calculations, and text extraction to `Dispatchers.IO`.
- Wrapped UI updates in `updateSelectionVisuals` and selection logic with `withContext(Dispatchers.Main)`.
- Implemented a more efficient `Popup`-based magnifier to replace manual offsets and transformations.
- Updated `PdfSelectionMenuPopup` properties to prevent focus and click-outside dismissal conflicts.

app/src/main/java/com/aryan/reader/epubreader/EpubReaderScreen.kt

@@ -363,7 +363,16 @@ fun EpubReaderScreen(
         onRenderModeChange = onRenderModeChange,
         customFonts = customFonts,
         onImportFont = onImportFont,
-        onToggleReflow = onOpenOriginal
+        onToggleReflow = onOpenOriginal,
+        onDeleteReflow = if (isReflowFile) {
+            {
+                uiState.selectedBookId?.let { id ->
+                    viewModel.deleteBookPermanently(id) {
+                        onNavigateBack()
+                    }
+                }
+            }
+        } else null
     )
 }
 
@@ -388,7 +397,8 @@ fun EpubReaderHost(
     onRenderModeChange: (RenderMode) -> Unit,
     customFonts: List<CustomFontEntity>,
     onImportFont: (Uri) -> Unit,
-    onToggleReflow: ((Int) -> Unit)? = null
+    onToggleReflow: ((Int) -> Unit)? = null,
+    onDeleteReflow: (() -> Unit)? = null
 ) {
     val view = LocalView.current
     val context = LocalContext.current
@@ -3124,6 +3134,7 @@ fun EpubReaderHost(
                             onToggleReflow(activeChapter)
                         }
                     } else null,
+                    onDeleteReflow = onDeleteReflow
                 )
 
                 val autoScrollPadding by androidx.compose.animation.core.animateDpAsState(