Wire loadPlugin(builtinPlugin) at editor app bootstrap

Adds apps/editor/lib/bootstrap.ts that calls loadPlugin(builtinPlugin)
as a module-side-effect on first import. Imported from scene-loader.tsx
so it runs on the client side where the editor mounts.

Idempotency guard handles HMR re-execution (would otherwise throw on
duplicate registerNode). For the empty plugin this commit, the entire
call is a no-op — included now so future commits that add real node
kinds only need to push them onto builtinPlugin.nodes.

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

bun.lock

@@ -31,6 +31,7 @@
         "@pascal-app/core": "*",
         "@pascal-app/editor": "*",
         "@pascal-app/mcp": "*",
+        "@pascal-app/nodes": "*",
         "@pascal-app/viewer": "*",
         "@radix-ui/react-tooltip": "^1.2.8",
         "@react-three/drei": "^10.7.7",