docs(book): Reformat chapters 18-19 with rich markdown

Complete penultimate chapters with comprehensive visual enhancements.

Chapter 18 (MEV Bundle Construction):
- 7+ Mermaid diagrams (timeline, flowcharts, sequences, pie/bar charts)
- 15+ tables (PBS architecture, tip optimization, bundle conflicts, metrics)
- 10+ callout boxes for MEV extraction mechanics and best practices
- Enhanced bundle construction algorithms with profitability analysis

Chapter 19 (Flash Loan Arbitrage):
- 6+ Mermaid diagrams (execution flows, timelines, attack patterns)
- 18+ tables (case studies, attack vectors, profitability, gas costs)
- Detailed coverage of major exploits (bZx, Cream Finance, Beanstalk)
- Complete OVSM implementation with multi-protocol flash loans

Both chapters feature:
- Real-world case studies with dollar amounts and timelines
- Risk analysis for failed transactions and attack patterns
- Production-grade OVSM code with gas optimization
- Comprehensive tables for strategy comparison

Progress: 9/10 strategy chapters complete (only Ch. 20 remaining)

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

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

Author: 0xrinegade