[jamiesun]

Changes

• Add production/assembly handoff guidance and fixed-revision commands in the workbench
• Inspect selected media, durations and audio bounds without mutations
• Preserve drafts and project authorization; document the filmkit boundary
• Simplify the user-facing README

Validation

• 103 integration tests and 27 Chromium tests passed locally
• Typecheck, lint and build passed
• Real cross-repository strict-project assembly and motion-reference checks passed
• No schema migration, production-data write, generation runtime or automatic sync