Add documentation for the new logging config options (output and level),
including usage examples, field reference table, and updated project
structure listing the internal/logging package.
- Fix metrics: change MessagesTotal, ConnectionsTotal, DisconnectionsTotal
from Gauge to Counter with proper _total naming convention
- Fix broadcast write-error handling: failed clients now get properly
removed with accurate metrics updates
- Add graceful shutdown: SIGINT/SIGTERM handling with 10s timeout,
CloseGoingAway frame sent to clients before disconnect
- Add integration tests: 11 tests using real WebSocket connections
covering connect, broadcast, disconnect, concurrency, and shutdown
- Fix example client port: changed from 8000 to 8443 to match config
- Rewrite README.md to reflect current features and usage
- Add AGENTS.md and .agents/summary/ documentation for AI assistants
