Add high-capacity server configuration and concurrent player emulator

Server optimizations for 390+ concurrent users:
- Increase HTTP thread pool: 500 max threads, 600 max accept
- SQLite performance tuning: 64MB cache, NORMAL sync, memory mapping
- Session optimization: frequent GC, disable URL rewriting
- Increase SQLite busy timeout to 30 seconds

Player emulator features:
- Concurrent execution with worst-case thundering herd testing
- Browser-like behavior: static files, login, WebSocket, challenge solving
- WebSocket message validation and detailed logging
- Realistic delays and batch flag submissions
- Supports N concurrent players via command line

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

Co-Authored-By: Claude <noreply@anthropic.com>