feat(highways): per-splitscreen-panel Camera Director cameras

Make the three 3D highways read the Camera Director bridge per panel so each
splitscreen panel renders its own camera (independent orbit/height/zoom/tilt/pan),
instead of all panels sharing the focused camera.

- Add a shared `_freeCamFor(canvas)` resolver to each highway: prefer this panel's
  entry in `window.__h3dCamCtlPanels[panelIndexFor(canvas)]`, fall back to the
  global `window.__h3dCamCtl`, else null (100% stock). Defensive on the splitscreen
  global name (feedBackSplitscreen || slopsmithSplitscreen), NaN-safe, allocation-free.
- highway_3d (guitar): source `_freeCam` from the resolver (was global-only).
- keys_highway_3d: adopt the bridge for the first time — layer dolly/height/orbit +
  pan/pitch offsets onto the pan/zoom follow rig at the camera write.
- drum_highway_3d: adopt the bridge — new per-frame `applyCamera()` folds the static
  base pose + kick-pulse dip + free-cam offsets.
- In a follower (popped-out) window there is one panel, so the resolver yields
  whatever camera the plugin set in that window; no highway change needed for pop-out.

Camera Director absent → resolver returns null → renderers behave exactly as before.
Bump each plugin patch version. Existing plugin tests pass (drum 15, keys 30); the
keys "default look unchanged" test confirms the stock path is byte-identical.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Signed-off-by: Kris Anderson <topkoa@gmail.com>

plugins/drum_highway_3d/plugin.json

@@ -1,7 +1,7 @@
 {
   "id": "drum_highway_3d",
   "name": "3D Drum Highway",
-  "version": "0.3.1",
+  "version": "0.3.2",
   "type": "visualization",
   "bundled": true,
   "script": "screen.js",