feat(editor): define OpenCut presentation and OpenScene project boundary

[sjungwon03]

Summary

• Pin reviewed Theorvane/OpenCut PR chore: gate main releases to dev promotion PRs #8 (56fd309f) and render its shared EditorHeader inside the OpenScene workbench.
• Pass the live OpenScene project name, theme values and callbacks, and save/export actions to the presentation component.
• Record the OpenCut presentation versus OpenScene project, edit, export, and Agent ownership boundary in the integration guide, glossary, and ADR.

Verification

• npm run typecheck
• npm test (236 files, 1,549 tests)
• npm run build
• cd mobile && npm run typecheck
• Electron smoke: open project, choose Midnight Neon, import MP4, place twice, select clips, observe monitor/filmstrip/waveform with no UI errors.
• OpenCut PR chore: gate main releases to dev promotion PRs #8: web/Bun CI on Ubuntu, Windows, macOS and AI code review approved.

Closes #476

[sjungwon03-ai]

Review summary

Verdict: Approved

• Reviewed: OpenCut header integration and the OpenScene/OpenCut ownership boundary
• Checks: CI passed; npm run typecheck, npm run build, and the targeted layout test passed.