docs: Add comprehensive PROJECT_INTERVIEW_GUIDE for interviews

Add detailed interview preparation guide covering:
- 4-phase pipeline architecture (Audio/Render/Export/2D)
- Configuration-first design patterns
- 7 Q&A across 5 themes (Architecture, Implementation, Testing, Challenges, Business)
- Real performance benchmarks (4 min → 50 min)
- Code references for every answer
- Trade-off analysis for key decisions
- Headless rendering deployment patterns
- Connection to Semantic Intent portfolio

Demonstrates senior-level engineering through:
- Pipeline architecture design
- Configuration-driven systems
- Blender automation mastery
- Cloud deployment readiness (Docker/AWS)
- Production-ready performance testing

Highlights unique differentiators:
- Configuration-first (YAML-driven, no code changes)
- 4-phase modular pipeline
- Headless rendering (Xvfb + Docker)
- Real benchmarks (4 min ultra-fast → 50 min production)
- Extensible plugin system

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: michshat