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/shortcuts/app_shortcuts.dart

@@ -7,8 +7,9 @@ import '../services/file_handler.dart';
 
 class AppShortcuts extends StatelessWidget {
   final Widget child;
+  final VoidCallback? onCropSave;
 
-  const AppShortcuts({super.key, required this.child});
+  const AppShortcuts({super.key, required this.child, this.onCropSave});
 
   @override
   Widget build(BuildContext context) {
@@ -35,6 +36,14 @@ class AppShortcuts extends StatelessWidget {
             return KeyEventResult.handled;
           }
 
+          // Ctrl+S: görünen alanı kaydet (crop save)
+          if (ctrl && !shift && event.logicalKey == LogicalKeyboardKey.keyS) {
+            if (onCropSave != null) {
+              onCropSave!();
+              return KeyEventResult.handled;
+            }
+          }
+
           switch (event.logicalKey) {
             case LogicalKeyboardKey.arrowLeft:
               ImageManager.instance.previousImage();