docs: Add comprehensive PROJECT_INTERVIEW_GUIDE for interviews

Add detailed interview preparation guide covering:
- 3-layer Wake Intelligence brain (Past/Present/Future)
- Technical architecture (hexagonal + temporal intelligence)
- 8 Q&A across 5 themes (Architecture, Implementation, Testing, Challenges, Business)
- Code references for every answer
- Trade-off analysis for key decisions
- Real problem-solving examples (prediction optimization, dependency detection)
- Testing strategy (109 tests breakdown)
- Connection to Semantic Intent portfolio

Demonstrates senior-level engineering through:
- Temporal intelligence system design
- Deterministic prediction algorithms
- Edge computing deployment (Cloudflare Workers)
- Comprehensive testing discipline
- Production-ready patterns

Highlights unique differentiators:
- 3-layer brain architecture (causality + memory + propagation)
- Composite prediction scoring (40% temporal + 30% causal + 30% frequency)
- 4-tier memory management (ACTIVE/RECENT/ARCHIVED/EXPIRED)
- 90% composition root reduction (74 lines)
- 109 comprehensive tests

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

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

Author: semanticintent