feat: vrai fondu enchaîné par overlay image sur le heatmap

Principe : capture du canvas heatmap actuel dans une <img> superposée
(opacity 1), mise à jour immédiate du heatmap en dessous, puis
dissolution de l'overlay (opacity 0 en 500ms). Les deux frames
coexistent pendant la transition → vrai dissolve sans clignotement.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/HeatMap.tsx

@@ -33,6 +33,7 @@ export function HeatMap({ transactions }: HeatMapProps) {
   const containerRef = useRef<HTMLDivElement>(null);
   const mapRef = useRef<L.Map | null>(null);
   const heatRef = useRef<L.HeatLayer | null>(null);
+  const overlayRef = useRef<HTMLImageElement | null>(null);
 
   // Initialize map once
   useEffect(() => {
@@ -64,11 +65,12 @@ export function HeatMap({ transactions }: HeatMapProps) {
     };
   }, []);
 
-  // Update heatmap data with fade transition when transactions change
+  // Crossfade: capture current heatmap → update underneath → fade out overlay
   useEffect(() => {
     if (!heatRef.current || !mapRef.current) return;
 
     const canvas = (heatRef.current as unknown as { _canvas?: HTMLCanvasElement })._canvas;
+    const overlay = overlayRef.current;
 
     const update = () => {
       const maxAmount = Math.max(...transactions.map((t) => t.amount), 1);
@@ -84,28 +86,45 @@ export function HeatMap({ transactions }: HeatMapProps) {
       }
     };
 
-    if (!canvas) {
+    if (!canvas || !overlay) {
       update();
       return;
     }
 
-    canvas.style.transition = 'opacity 0.15s ease-out';
-    canvas.style.opacity = '0.15';
-
-    const t = setTimeout(() => {
+    // Freeze current frame in the overlay
+    try {
+      overlay.src = canvas.toDataURL();
+    } catch {
+      // canvas tainted (shouldn't happen with heatmap-only canvas)
       update();
-      canvas.style.transition = 'opacity 0.2s ease-in';
-      canvas.style.opacity = '1';
-    }, 150);
+      return;
+    }
+    overlay.style.transition = 'none';
+    overlay.style.opacity = '1';
 
-    return () => clearTimeout(t);
+    // Update heatmap underneath immediately
+    update();
+
+    // Then dissolve the overlay away
+    const raf = requestAnimationFrame(() => {
+      requestAnimationFrame(() => {
+        overlay.style.transition = 'opacity 0.5s ease-in-out';
+        overlay.style.opacity = '0';
+      });
+    });
+
+    return () => cancelAnimationFrame(raf);
   }, [transactions]);
 
   return (
-    <div
-      ref={containerRef}
-      className="w-full h-full"
-      style={{ minHeight: 0 }}
-    />
+    <div className="w-full h-full relative" style={{ minHeight: 0 }}>
+      <div ref={containerRef} className="absolute inset-0" />
+      <img
+        ref={overlayRef}
+        alt=""
+        className="absolute inset-0 w-full h-full pointer-events-none"
+        style={{ opacity: 0, zIndex: 500 }}
+      />
+    </div>
   );
 }