docs: Add comprehensive pipeline test evaluation report

Complete evaluation of full pipeline test in cloud environment:
- All 3 phases completed successfully (Audio Prep, Rendering, Export)
- Visual verification confirms lyrics positioning fix works
- Lyrics now appear in lower third, clearly visible in front of mascot
- 360 frames rendered at 180p (ultra-fast config)
- Performance metrics: ~4-5 minutes total for 30s song
- Detailed analysis of lip sync, beat gestures, and lyrics timing
- Documentation of headless rendering setup (Blender + Xvfb)
- Recommendations for next steps (quick test, debug mode, production)

Test results validate all recent code changes.

Author: claude