Refactor Zoodle into runtime scene extension

[franknoirot]

Summary

• Add a runtime engine-scene extension slot to the app registry roots.
• Move Zoodle activation from local React overlay state to a runtime extension that contributes a stream class name and stream layer.
• Render the existing annotation overlay in-place as an engine-scene stream layer while preserving the current drawing, clear, cancel, and send behavior.

Stacked on #12282 (franknoirot/adhoc/engine-scene-extensions). This PR is intended to be behavior-preserving; the inset transition and additional drawing tools are left for follow-up PRs.

Testing

• npx biome check --formatter-enabled=true --linter-enabled=false --organize-imports-enabled=true --files-ignore-unknown=true src/components/MlEphantConversation.tsx src/components/MlEphantConversation.spec.tsx src/components/ViewportAnnotationOverlay.tsx src/components/layout/areas/MlEphantConversationPane.spec.tsx src/lib/app.ts src/registry/contracts/engineScene.tsx src/registry/extensions/engineScene/zoodleRuntimeExtension.tsx
• npx vitest run --mode=development src/components/MlEphantConversation.spec.tsx src/components/layout/areas/MlEphantConversationPane.spec.tsx src/registry/extensions/engineScene/index.spec.ts
• npm run tsc -- --noEmit

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Project	Deployment	Actions	Updated (UTC)
modeling-app	Ready	Preview, Comment	Jun 30, 2026 6:56pm