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.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+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'**
   String get shortcutsList;
 
   /// No description provided for @print.
@@ -152,6 +152,36 @@ abstract class AppLocalizations {
   /// **'Close'**
   String get close;
 
+  /// No description provided for @saveCrop.
+  ///
+  /// In en, this message translates to:
+  /// **'Save visible area (JPEG 90)'**
+  String get saveCrop;
+
+  /// No description provided for @cropSaved.
+  ///
+  /// In en, this message translates to:
+  /// **'Saved: {path}'**
+  String cropSaved(String path);
+
+  /// No description provided for @cropFileExists.
+  ///
+  /// In en, this message translates to:
+  /// **'A file with the same name already exists — nothing was written'**
+  String get cropFileExists;
+
+  /// No description provided for @cropUnsupported.
+  ///
+  /// In en, this message translates to:
+  /// **'This image format cannot be saved as a crop'**
+  String get cropUnsupported;
+
+  /// No description provided for @cropFailed.
+  ///
+  /// In en, this message translates to:
+  /// **'Failed to save crop'**
+  String get cropFailed;
+
   /// No description provided for @dragDropHint.
   ///
   /// In en, this message translates to: