Position persistence during orientation change (#64)

* Fixed PDF reading position restoration during orientation change

* Refactored navigation logic in `EpubReaderScreen` and `PaginatedReader` to improve position restoration and UI consistency.

- Renamed `isNavigatingToBookmark` to `isNavigatingToPosition` and updated the overlay UI to reflect general position navigation.
- Added an orientation change listener to restore the reading position in `VERTICAL_SCROLL` mode using the last known locator.
- Improved highlight navigation in `VERTICAL_SCROLL` and `PAGINATED` modes, including chunk injection logic for highlights and fallback pagination logic.
- Implemented an anchor locator mechanism in `PaginatedReader` to preserve the reading position during layout constraint changes (e.g., orientation or resizing).

app/src/main/java/com/aryan/reader/MainActivity.kt

@@ -69,7 +69,9 @@ class MainActivity : ComponentActivity() {
             }
         }
 
-        handleIntent(intent)
+        if (savedInstanceState == null) {
+            handleIntent(intent)
+        }
 
         lifecycleScope.launch {
             platformFeaturesRepository.checkForUpdates(this@MainActivity, updateLauncher)