feat(export): add final video and Remotion rendering

[JustinPerea]

What changed

• Added final Video Editor exports for MP4/H.264, MOV/ProRes 422 HQ, WebM/VP9, and animated GIF with resolution and quality controls.
• Replaced the Remotion node's preview-only backend with a real local H.264 renderer using the same composition and exact { manifest } input props as the Player.
• Added shared render-job progress, cancellation, download, partial-file cleanup, and UI controls for both editor surfaces.
• Declared hidden runtime editor params so clip state and Remotion manifests persist through the graph API.
• Pinned the full Remotion package family to 4.0.479 and documented the runtime and license boundary.

Why

The editors could preview work but did not have a complete final-delivery path. The Remotion graph handler also returned no rendered video. This closes both gaps with local renders and no provider inference cost.

Validation

• Backend: 1,197 passed, with two existing AsyncMock warnings.
• Frontend: 402 passed, lint, TypeScript, and production build passed.
• Node contracts: 142 definitions passed; generated model reference is current.
• Dependency audit: zero findings.
• Live UI: 1080p WebM completion/download, progress and cancellation with no partial file, and a 5.056 s Remotion H.264/AAC MP4 at 1280x720 and 30 fps.
• Multiformat ffmpeg smoke: H.264/AAC MP4, ProRes/PCM MOV, VP9/Opus WebM, and GIF.
• git diff --check and staged credential scans passed.
• No paid provider call ran.

Known non-blocking finding

scripts/check-utility-nodes.mjs repeatedly timed out waiting for its unrelated pure-utility browser graph after the backend logged that execution as completed. This PR does not touch that execution-event/store path, and the backend/frontend suites covering it pass. The finding is carried into the run-history follow-up.