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

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 {
-  ChatZoomWrapper({super.key, required this.child, this.onDoubleTap});
+class ChatZoomWrapper extends StatefulWidget {
+  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;
-}