docs: Add comprehensive AST analysis enhancement proposal

Created two detailed documents:

1. AST_ANALYSIS_ENHANCEMENT_PROPOSAL.md
   - Executive summary of current AST capabilities
   - Proposed enhancements for all 6 gears
   - New tools: API inventory, business logic map, code-to-spec linker
   - Implementation phases and technical architecture
   - Success metrics and risks

2. AST_PRACTICAL_EXAMPLE.md
   - Real-world example using e-commerce API
   - Shows exact AST output for each gear
   - Before/after comparison (2hrs manual vs 5min automated)
   - Demonstrates 95% time savings, 100% accuracy

Current AST capabilities (already built):
- Function signature extraction
- Class declaration parsing
- Import/export mapping
- Stub detection
- Doc comment extraction
- Used in: gap-analyzer, feature-analyzer, diagram generation

Proposed enhancements:
- Gear 1: API endpoint extraction, middleware chains
- Gear 2: Business logic patterns, data flow tracing
- Gear 3: Auto-generated specs with actual signatures
- Gear 4: Signature validation, error handling checks
- Gear 5: Evidence-based clarifications
- Gear 6: Automated implementation verification

ROI: 10x faster analysis, 95%+ accuracy, zero spec drift

Author: jschulte