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/screens/viewer_screen.dart

@@ -8,6 +8,7 @@ import 'package:pdf/widgets.dart' as pw;
 import 'package:printing/printing.dart';
 import '../services/image_manager.dart';
 import '../services/file_handler.dart';
+import '../services/crop_save_service.dart';
 import '../widgets/custom_title_bar.dart';
 import '../widgets/image_canvas.dart';
 import '../widgets/window_resize_zones.dart';
@@ -28,6 +29,7 @@ class _ViewerScreenState extends State<ViewerScreen> with WindowListener {
   bool _controlsVisible = false;
   Timer? _saveDebounce;
   Rect _lastBounds = Rect.zero;
+  final GlobalKey<ImageCanvasState> _canvasKey = GlobalKey<ImageCanvasState>();
 
   @override
   void initState() {
@@ -188,9 +190,53 @@ class _ViewerScreenState extends State<ViewerScreen> with WindowListener {
     );
   }
 
+  Future<void> _cropSave() async {
+    final path = ImageManager.instance.currentImagePath;
+    final state = _canvasKey.currentState;
+    if (path.isEmpty || state == null) return;
+    final l10n = AppLocalizations.of(context)!;
+    String? message;
+    try {
+      final source = await CropSaveService.load(path);
+      final rect = state.cropSourceRect(source.width, source.height);
+      if (rect == null || rect.isEmpty || !rect.isFinite) {
+        message = l10n.cropFailed;
+      } else {
+        final outPath = await CropSaveService.saveCrop(
+          srcPath: path,
+          source: source,
+          rect: rect,
+          matrix: state.activeColorMatrix,
+        );
+        message = l10n.cropSaved(outPath);
+      }
+    } on CropSaveError catch (e) {
+      switch (e.code) {
+        case 'file_exists':
+          message = l10n.cropFileExists;
+        case 'decode':
+          message = l10n.cropUnsupported;
+        default:
+          message = l10n.cropFailed;
+      }
+    } catch (_) {
+      message = l10n.cropFailed;
+    }
+    if (!mounted) return;
+    ScaffoldMessenger.of(context)
+      ..hideCurrentSnackBar()
+      ..showSnackBar(SnackBar(
+        content: Text(message, style: const TextStyle(fontSize: 13)),
+        duration: const Duration(seconds: 2),
+        behavior: SnackBarBehavior.floating,
+        width: 520,
+      ));
+  }
+
   @override
   Widget build(BuildContext context) {
     return AppShortcuts(
+      onCropSave: _hasImages ? _cropSave : null,
       child: Scaffold(
         backgroundColor: Colors.transparent,
         body: WindowResizeZones(
@@ -223,6 +269,7 @@ class _ViewerScreenState extends State<ViewerScreen> with WindowListener {
                       color: Colors.transparent,
                       child: _hasImages
                           ? ImageCanvas(
+                              key: _canvasKey,
                               filePath: ImageManager.instance.currentImagePath,
                             )
                           : Center(
@@ -242,6 +289,7 @@ class _ViewerScreenState extends State<ViewerScreen> with WindowListener {
                   ),
                   CustomTitleBar(
                     onSettings: _showSettings,
+                    onSaveCrop: _hasImages ? _cropSave : null,
                     visible: _controlsVisible,
                   ),
                   if (_hasImages && _controlsVisible) ...[