feat: add CSS Animation Editor tool

Comprehensive visual editor for CSS @keyframe animations:
- AnimationSettings: name, duration, delay, easing (incl. cubic-bezier), iteration, direction, fill-mode
- KeyframeTimeline: drag-to-reposition keyframe markers, click-track to add, delete selected
- KeyframeProperties: per-keyframe transform (translate/rotate/scale/skew), opacity, background-color, border-radius, blur, brightness via sliders
- AnimationPreview: live preview on box/circle/text element with play/pause/restart and speed control (0.25×–2×)
- PresetLibrary: 22 presets across Entrance/Exit/Attention/Special categories with animated thumbnails
- ExportPanel: plain CSS and Tailwind v4 @utility formats with copy and download

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

app/(app)/animate/page.tsx

@@ -0,0 +1,16 @@
+import type { Metadata } from 'next';
+import { AnimationEditor } from '@/components/animate/AnimationEditor';
+import { AppPage } from '@/components/layout/AppPage';
+import { getToolByHref } from '@/lib/tools';
+
+const tool = getToolByHref('/animate')!;
+
+export const metadata: Metadata = { title: tool.title, description: tool.summary };
+
+export default function AnimatePage() {
+  return (
+    <AppPage title={tool.title} description={tool.summary} icon={tool.icon}>
+      <AnimationEditor />
+    </AppPage>
+  );
+}