0.13.0: unify all track kinds — same height, same drag, same grouping

- Scripts bumped from 26px to 30px so the five track kinds read as one
  visual list; clip / script / audio tracks lose their kind-specific
  gradient backgrounds now that they're no longer fixed-position
  chrome.
- Audio tracks pick up the standard drag attributes + handlers; they
  now participate in the same trackOrder flow as layer / clip / script
  tracks and can be dropped into groups.
- normalizeScenePage accepts scripts + audio as group children (used
  to silently strip them); the per-kind ordered appending is replaced
  with a single tail loop so no kind is hardcoded to the bottom.
- moveTrackIntoGroup color cascade now covers all four groupable kinds
  (scripts + audio inherit group colour like layers + clip tracks).
- Group expansion in Timeline emits scripts + audio as first-class
  sub-track children, with the shared in-group / sub-track classes
  and group-aware drag handlers.
- Tests: move-into-group + color cascade for scripts + audio, legacy
  childIds roundtrip preserves both kinds, audio track is draggable,
  script track is 30px.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -1,7 +1,7 @@
 {
   "name": "ruwio",
   "private": true,
-  "version": "0.12.0",
+  "version": "0.13.0",
   "type": "module",
   "scripts": {
     "dev": "vite",