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>

lib/animate/defaults.ts

@@ -0,0 +1,47 @@
+import type { AnimationConfig, Keyframe, TransformValue } from '@/types/animate';
+
+export const DEFAULT_TRANSFORM: TransformValue = {
+  translateX: 0,
+  translateY: 0,
+  rotate: 0,
+  scaleX: 1,
+  scaleY: 1,
+  skewX: 0,
+  skewY: 0,
+};
+
+export function newKeyframe(offset: number): Keyframe {
+  return {
+    id: crypto.randomUUID(),
+    offset,
+    properties: {},
+  };
+}
+
+export const DEFAULT_CONFIG: AnimationConfig = {
+  name: 'fadeInUp',
+  duration: 600,
+  delay: 0,
+  easing: 'ease-out',
+  iterationCount: 1,
+  direction: 'normal',
+  fillMode: 'forwards',
+  keyframes: [
+    {
+      id: crypto.randomUUID(),
+      offset: 0,
+      properties: {
+        opacity: 0,
+        transform: { ...DEFAULT_TRANSFORM, translateY: 20 },
+      },
+    },
+    {
+      id: crypto.randomUUID(),
+      offset: 100,
+      properties: {
+        opacity: 1,
+        transform: { ...DEFAULT_TRANSFORM },
+      },
+    },
+  ],
+};