Feature/highlighter snap (#48)

* perf: fix Home and Library screen stutter by removing main thread file checks

* feat(pdf): implement straight-line highlighter snap

- Added "Straight Line" toggle to highlighter settings popup with persistent state.
- Implemented "rubber-band" drawing effect for highlighters with cardinal direction snapping (0°, 90°, 180°, 270°).
- Optimized gesture loops in Vertical and Paginated readers to respond instantly to setting toggles.
- Rewrote eraser hit detection using point-to-line segment distance math for pixel-perfect erasure of straight lines.

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

@@ -417,7 +417,8 @@ internal fun PdfPageComposable(
     draggingBoxId: String? = null,
     isScrollLocked: Boolean = false,
     isVisible: Boolean = true,
-    isStylusOnlyMode: Boolean = false
+    isStylusOnlyMode: Boolean = false,
+    isHighlighterSnapEnabled: Boolean = false
 ) {
     SideEffect { Timber.tag("PdfDrawPerf").v("PdfPageComposable Recompose: Page $pageIndex") }
     val pdfDocumentItem = pdfDocument.item
@@ -2608,7 +2609,8 @@ internal fun PdfPageComposable(
                 isScrolling,
                 isVerticalScroll,
                 selectedTool,
-                isStylusOnlyMode
+                isStylusOnlyMode,
+                isHighlighterSnapEnabled
             ) {
                 val canDraw = isEditMode && selectedTool != InkType.TEXT && !isScrolling && !isVerticalScroll && actualBitmapWidthPx > 0 && actualBitmapHeightPx > 0
 
@@ -4611,6 +4613,16 @@ class PdfDrawingState {
         currentPoints.clear()
         return finalAnnot
     }
+
+    fun updateDrag(point: PdfPoint) {
+        if (currentPoints.isNotEmpty()) {
+            val start = currentPoints.first()
+            currentPoints.clear()
+            currentPoints.add(start)
+            currentPoints.add(point)
+            currentAnnotation = currentAnnotation?.copy(points = currentPoints.toList())
+        }
+    }
 }
 
 @Composable