feat(frontend): content micro-animations — stagger, button press, toast polish

- animate-stagger utility + staggerDelay() helper; lists now rise in sequence
  (recordings grid, moderation rows, message list, media queue, dashboard tiles).
- Button gets a subtle active:scale-[0.97] press feedback.
- Toaster: toast-in slide-up, tone-accent border, rounded hover-close target.
- All motion is reduced-motion aware (killed under prefers-reduced-motion).

services/frontend/src/lib/utils.ts

@@ -4,3 +4,16 @@ import { twMerge } from "tailwind-merge";
 export function cn(...inputs: ClassValue[]) {
   return twMerge(clsx(inputs));
 }
+
+/**
+ * Returns an inline style that staggers a list item's entrance animation.
+ * Pair with the `animate-stagger` class. Caps the delay so long lists still
+ * appear promptly.
+ */
+export function staggerDelay(
+  index: number,
+  step = 45,
+  max = 600,
+): React.CSSProperties {
+  return { animationDelay: `${Math.min(index * step, max)}ms` };
+}