feat: downsampling + full-res swap + RAM leak fix

- Büyük resimler ilk yüklemede max 2048px'e downsampling (RAM ~1.6MB)
- Zoom 1.5x stretch'i geçince full-res'e swap (orijinal çözünürlük)
- Resim geçişinde eski provider evict + ImageCache.evict() (RAM leak)
- Tiled render kodu tamamen kaldırıldı

lib/widgets/image_canvas.dart

@@ -39,6 +39,11 @@ class _ImageCanvasState extends State<ImageCanvas> {
   bool _ctrlPressed = false;
   bool _shiftPressed = false;
 
+  // ── Downsampling + swap ──
+  bool _usingFullRes = false;
+  Size _imageSize = Size.zero;
+  static const int _downsampleTarget = 2048;
+
   // ── Kare hızına eşitlenmiş render tick ──
   final ValueNotifier<int> _renderTick = ValueNotifier(0);
   bool _frameScheduled = false;
@@ -179,12 +184,22 @@ class _ImageCanvasState extends State<ImageCanvas> {
   @override
   void didUpdateWidget(ImageCanvas old) {
     super.didUpdateWidget(old);
-    if (old.filePath != widget.filePath) _resetView();
+    if (old.filePath != widget.filePath) {
+      _cachedFileImage?.evict();
+      _cachedProvider?.evict();
+      _cachedFileImage = null;
+      _cachedProvider = null;
+      _cachedPath = null;
+      _cachedCacheWidth = null;
+      PaintingBinding.instance.imageCache.evict(FileImage(File(old.filePath)));
+      _resetView();
+    }
   }
 
   void _resetView() {
     _tx = 0; _ty = 0; _sc = 1.0; _isFilled = true;
     _angle = 0; _contrast = 1.0; _saturation = 1.0; _brightness = 0;
+    _usingFullRes = false;
     _markRenderDirty();
   }
 
@@ -216,6 +231,7 @@ class _ImageCanvasState extends State<ImageCanvas> {
       _ty -= dh / 2;
     }
     _sc = newSc;
+    _checkFullResSwap();
     _clamp();
     _markRenderDirty();
   }
@@ -372,16 +388,29 @@ class _ImageCanvasState extends State<ImageCanvas> {
   String? _cachedPath;
   int? _cachedCacheWidth;
 
+  void _checkFullResSwap() {
+    if (_usingFullRes || _imageSize.isEmpty) return;
+    final double stretchX = _vpSize.width * _sc / _imageSize.width;
+    final double stretchY = _vpSize.height * _sc / _imageSize.height;
+    if (math.max(stretchX, stretchY) >= 1.5) {
+      setState(() {
+        _usingFullRes = true;
+        _cachedProvider = _cachedFileImage;
+        _cachedCacheWidth = null;
+      });
+    }
+  }
+
   Widget _buildImage() {
-    final longest = _vpSize.longestSide;
-    final cacheWidth = longest > 0 ? (longest * _sc * 2).round() : null;
-    if (_cachedPath != widget.filePath || _cachedCacheWidth != cacheWidth) {
+    final needFullRes = _usingFullRes;
+    final effectiveWidth = needFullRes ? null : _downsampleTarget;
+    if (_cachedPath != widget.filePath || _cachedCacheWidth != effectiveWidth) {
       _cachedPath = widget.filePath;
-      _cachedCacheWidth = cacheWidth;
+      _cachedCacheWidth = effectiveWidth;
       _cachedFileImage = FileImage(File(widget.filePath));
-      _cachedProvider = cacheWidth != null
-          ? ResizeImage.resizeIfNeeded(cacheWidth, null, _cachedFileImage!)
-          : null;
+      _cachedProvider = effectiveWidth != null
+          ? ResizeImage.resizeIfNeeded(effectiveWidth, null, _cachedFileImage!)
+          : _cachedFileImage;
     }
     final ImageProvider<Object> provider = _cachedProvider ?? _cachedFileImage!;
     return Image(
@@ -391,6 +420,18 @@ class _ImageCanvasState extends State<ImageCanvas> {
       filterQuality: FilterQuality.high,
       gaplessPlayback: true,
       errorBuilder: (_, _, _) => _errorWidget(),
+      loadingBuilder: (context, child, loadingProgress) {
+        if (loadingProgress == null && _imageSize.isEmpty) {
+          provider.resolve(const ImageConfiguration()).addListener(
+            ImageStreamListener((info, _) {
+              if (_imageSize.isEmpty) {
+                _imageSize = Size(info.image.width.toDouble(), info.image.height.toDouble());
+              }
+            }),
+          );
+        }
+        return child;
+      },
     );
   }