perf(editor): stabilize viewer stage mode sets

[Aymericr]

What does this PR do?

Makes normalizeViewerStageModes return canonical, referentially stable mode combinations. This keeps documented inline arrays such as modes={['3d', '2d']} from rebuilding ViewerStage callbacks and media-query effects whenever a host rerenders.

How to test

1. Run bun --cwd packages/editor check-types.
2. Run bun test packages/editor/src/components/viewer/viewer-stage-modes.test.ts packages/editor/src/components/viewer/viewer-stage.test.tsx.
3. Confirm equivalent mode arrays normalize to the same reference.

Screenshots / screen recording

Not applicable; this is a behavior-preserving performance cleanup.

Checklist

• I've tested this locally with bun dev
• My code follows the existing code style (run bun check to verify)
• I've updated relevant documentation (if applicable)
• This PR targets the main branch