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_en.dart

@@ -29,7 +29,7 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get shortcutsList =>
-      '• 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';
 
   @override
   String get print => 'Print';
@@ -38,7 +38,7 @@ class AppLocalizationsEn extends AppLocalizations {
   String get close => 'Close';
 
   @override
-  String get saveCrop => 'Save visible area (JPEG 90)';
+  String get saveCrop => 'Save visible area (JPEG 93)';
 
   @override
   String cropSaved(String path) {