refactor(frontend): lint, one session guard, one request helper, one user context

src/components/Confetti.jsx

@@ -49,6 +49,9 @@ function pieces(size, width, height) {
 export default function Confetti({size, onDone}) {
     const canvasRef = useRef(null);
     const [reduce] = useState(reducedMotion);
+    // In a ref: a new function from a re-render must not restart the animation, and the latest one runs at the end.
+    const onDoneRef = useRef(onDone);
+    onDoneRef.current = onDone;
 
     useEffect(() => {
         const canvas = canvasRef.current;
@@ -67,7 +70,7 @@ export default function Confetti({size, onDone}) {
             context.setTransform(1, 0, 0, 1, 0, 0);
             context.clearRect(0, 0, canvas.width, canvas.height);
             if (elapsed >= DURATION_MS) {
-                onDone?.();
+                onDoneRef.current?.();
                 return;
             }
             context.globalAlpha = 1 - elapsed / DURATION_MS;
@@ -88,7 +91,6 @@ export default function Confetti({size, onDone}) {
         };
         frame = requestAnimationFrame(draw);
         return () => cancelAnimationFrame(frame);
-        // Not on onDone: a new function from a re-render must not restart the animation.
     }, [size]);
 
     if (reduce) return null;