fix: timeline resize regression + dynamic lane alignment

- Remove splitAreaEl dependency from handleResizeMove; use fixed 40-500 clamp
- Add computeLanes() + LaneLayout for dynamic lane height computation
- Update clipRenderer to accept LaneLayout instead of hardcoded constants
- Tighten CONTROLS_HEIGHT (30→22) and CLIP_HEIGHT (30→20) to reduce gaps
- Tighten label baseline offset (14→10) for better waveform-to-tick alignment

Co-authored-by: Cursor <cursoragent@cursor.com>

src/lib/components/Timeline.svelte

@@ -10,7 +10,7 @@
     markOutPoint,
     removeClip,
   } from '$lib/stores/clips.svelte';
-  import { drawTimeline, type TimelineState } from '$lib/timeline/renderer';
+  import { drawTimeline, type TimelineState, computeLanes } from '$lib/timeline/renderer';
   import {
     computeZoom,
     panBy,
@@ -300,7 +300,7 @@
     const x = getCanvasX(e);
     const y = getCanvasY(e);
 
-    const hit = hitTestClip(x, y, timelineState, clipStore.clips);
+    const hit = hitTestClip(x, y, timelineState, clipStore.clips, computeLanes(timelineState.height));
     if (hit) {
       if (hit.edge === 'body') {
         selectClip(hit.clipId);