fix: crop save always JPEG q93 + save rotated view 1:1 (v1.4.1)

- Output extension is always .jpg regardless of source format (was: PNG in -> PNG out)
- Rotation now saved correctly: viewport grid resampled bilinearly in source
  space (was: unrotated bounding box copy)
- Quality 90 -> 93; l10n strings updated (JPEG 93)
- New: tool/crop_test.dart — pure-Dart end-to-end test (dart run tool/crop_test.dart)

lib/l10n/app_localizations.dart

@@ -137,7 +137,7 @@ abstract class AppLocalizations {
   /// No description provided for @shortcutsList.
   ///
   /// In en, this message translates to:
-  /// **'• Left/Right arrow — previous/next image\n• Ctrl+S — save visible area (JPEG 90)\n• Ctrl+Q — close window\n• Ctrl+Shift+Q — close all windows\n• Double click — toggle fill/fit\n• Right-drag — contrast\n• Shift+right-drag — rotate\n• Ctrl+right-drag — saturation\n• Ctrl+Shift+right-drag — brightness'**
+  /// **'• Left/Right arrow — previous/next image\n• Ctrl+S — save visible area (JPEG 93)\n• Ctrl+Q — close window\n• Ctrl+Shift+Q — close all windows\n• Double click — toggle fill/fit\n• Right-drag — contrast\n• Shift+right-drag — rotate\n• Ctrl+right-drag — saturation\n• Ctrl+Shift+right-drag — brightness'**
   String get shortcutsList;
 
   /// No description provided for @print.
@@ -155,7 +155,7 @@ abstract class AppLocalizations {
   /// No description provided for @saveCrop.
   ///
   /// In en, this message translates to:
-  /// **'Save visible area (JPEG 90)'**
+  /// **'Save visible area (JPEG 93)'**
   String get saveCrop;
 
   /// No description provided for @cropSaved.