fix(chat): stabilize pinch-to-zoom scaling

lib/services/chat_text_scale_service.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:flutter/foundation.dart';
 
 import '../storage/prefs_manager.dart';
@@ -21,6 +23,7 @@ class ChatTextScaleService extends ChangeNotifier {
   static const double _maxScale = 1.8;
 
   double _scale = 1.0;
+  Timer? _saveTimer;
 
   double get scale => _scale;
 
@@ -31,15 +34,39 @@ class ChatTextScaleService extends ChangeNotifier {
     }
   }
 
-  void setScale(double value) {
+  void setScale(double value, {bool persistImmediately = false}) {
     final next = _clamp(value);
     if (next == _scale) return;
     _scale = next;
-    PrefsManager.instance.setDouble(_prefKey, _scale);
     notifyListeners();
+    if (persistImmediately) {
+      _commitScale();
+    } else {
+      _scheduleSave();
+    }
   }
 
-  void reset() => setScale(1.0);
+  void reset() {
+    setScale(1.0, persistImmediately: true);
+  }
+
+  void persist() => _commitScale();
+
+  @override
+  void dispose() {
+    _saveTimer?.cancel();
+    super.dispose();
+  }
+
+  void _scheduleSave() {
+    _saveTimer?.cancel();
+    _saveTimer = Timer(const Duration(milliseconds: 250), _commitScale);
+  }
+
+  void _commitScale() {
+    _saveTimer?.cancel();
+    PrefsManager.instance.setDouble(_prefKey, _scale);
+  }
 
   double _clamp(double value) => value.clamp(_minScale, _maxScale).toDouble();
 }

lib/widgets/chat_zoom_wrapper.dart

@@ -6,12 +6,18 @@ import '../services/chat_text_scale_service.dart';
 /// Gesture wrapper that exposes two-finger pinch-to-zoom for chat scrollables.
 /// Double-tap resets the scale. Only the wrapper itself listens to gestures;
 /// child scrollables keep their normal touch handling.
-class ChatZoomWrapper extends StatelessWidget {
+class ChatZoomWrapper extends StatefulWidget {
-  ChatZoomWrapper({super.key, required this.child, this.onDoubleTap});
+  const ChatZoomWrapper({super.key, required this.child, this.onDoubleTap});
 
   final Widget child;
   final VoidCallback? onDoubleTap;
-  final _ZoomGestureState _state = _ZoomGestureState();
+
+  @override
+  State<ChatZoomWrapper> createState() => _ChatZoomWrapperState();
+}
+
+class _ChatZoomWrapperState extends State<ChatZoomWrapper> {
+  double? _startScale;
 
   @override
   Widget build(BuildContext context) {
@@ -21,25 +27,23 @@ class ChatZoomWrapper extends StatelessWidget {
       behavior: HitTestBehavior.translucent,
       onDoubleTap: () {
         service.reset();
-        onDoubleTap?.call();
+        service.persist();
+        widget.onDoubleTap?.call();
       },
       onScaleStart: (details) {
         if (details.pointerCount != 2) return;
-        _state.startScale = service.scale;
+        _startScale = service.scale;
       },
       onScaleUpdate: (details) {
         if (details.pointerCount != 2) return;
-        final baseScale = _state.startScale ?? service.scale;
+        final baseScale = _startScale ?? service.scale;
         service.setScale(baseScale * details.scale);
       },
       onScaleEnd: (_) {
-        _state.startScale = null;
+        _startScale = null;
+        service.persist();
       },
-      child: child,
+      child: widget.child,
     );
   }
 }
-
-class _ZoomGestureState {
-  double? startScale;
-}