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/components/primitives/button.tsx

@@ -40,7 +40,7 @@ export const Button = ({
   return (
     <Comp
       className={cn(
-        "inline-flex items-center justify-center whitespace-nowrap transition-all duration-150 select-none",
+        "inline-flex items-center justify-center whitespace-nowrap transition-all duration-150 select-none active:scale-[0.97]",
         "focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-signal/60 disabled:opacity-40 disabled:pointer-events-none",
         variants[variant],
         sizes[size],