[PERF] TimelineElement not wrapped in React.memo causes thousands of unnecessary re-renders

Description

apps/web/src/components/editor/panels/timeline/timeline-element.tsx is NOT wrapped in React.memo(). This is the most performance-critical component in the editor - it renders for every clip on the timeline.

Impact

Every playhead update triggers re-render of ALL visible timeline elements. With 100 tracks and 50+ elements each, this causes 5000+ unnecessary renders per update.

Additional Issues in Same Area

• Track array is cloned and sorted on every render in timeline/index.tsx:428-440 — should be wrapped in useMemo
• getKeyframeIndicators() recalculates on every render for selected elements (line 245-255)

Fix

1. Wrap TimelineElement with React.memo() with stable deps
2. Memoize the track sort in timeline/index.tsx with useMemo
3. Memoize keyframe indicator calculations

Files

• apps/web/src/components/editor/panels/timeline/timeline-element.tsx:186-368
• apps/web/src/components/editor/panels/timeline/index.tsx:428-440

Start with apps/web/src/components/editor/panels/timeline/timeline-element.tsx:186-368 and apps/web/src/components/editor/panels/timeline/index.tsx:428-440. Inspect the component updates, track sorting, and getKeyframeIndicators() calculations, then verify that TimelineElement is memoized and the listed work is complete without changing timeline behavior.