feat: crop save (save visible area at original resolution) v1.4.0

- Save visible area at original resolution as JPEG q90 (title bar button or Ctrl+S)
- Output name: original name + _HHmmss suffix; no overwrite, warning shown
- Active color effects baked in; rotation saves bounding box
- New: crop_save_service, l10n strings TR/EN, docs/plan-crop-save.md

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+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 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';
 
   @override
   String get print => 'Print';
@@ -37,6 +37,24 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get close => 'Close';
 
+  @override
+  String get saveCrop => 'Save visible area (JPEG 90)';
+
+  @override
+  String cropSaved(String path) {
+    return 'Saved: $path';
+  }
+
+  @override
+  String get cropFileExists =>
+      'A file with the same name already exists — nothing was written';
+
+  @override
+  String get cropUnsupported => 'This image format cannot be saved as a crop';
+
+  @override
+  String get cropFailed => 'Failed to save crop';
+
   @override
   String get dragDropHint => 'Drag images here\nor press Ctrl+O to open';