Improve timeline metadata probing for exports

[DeiElecti]

Summary

• parse FFmpeg log output in getVideoInfo with a DOM-based fallback to return real video duration, dimensions, and frame rate data
• add a reusable loadVideoMetadata helper and apply it while sizing timeline renders, including sorting audio clips and filling trailing gaps with blank segments
• refine audio mixing filters to use fractional padding durations for more accurate WebM exports

Testing

• npm run lint (fails: sh: 1: next: not found)

---

https://chatgpt.com/codex/tasks/task_e_68595dee4d288331a1d7a2545b5f9499