refactor: reorganize project into src layout and update API documentation

Update project structure to use a src/ directory layout and
improve documentation across multiple files.

- Update README.md build command to use ./src
- Add directory structure documentation
- Update status endpoint to include DB health status
- Add pagination support (limit/offset) to whitelist list endpoints
- Document new query parameters with examples
- Update deployment guide to mark API token as required
- Add testing instructions
- Clarify audit log rotation in design documentation

docs/deploy.md

@@ -83,11 +83,17 @@ nginx -s reload
 | Variable | Description | Default |
 |----------|-------------|---------|
 | AUTH_PROXY_PORT | HTTP listen port | 8080 |
-| AUTH_PROXY_API_TOKEN | API bearer token | (none) |
+| AUTH_PROXY_API_TOKEN | API bearer token | (required) |
 | AUTH_PROXY_DB_PATH | SQLite database path | /data/auth-proxy.db |
 | DATA_DIR | Data directory | /data |
 | CLEANUP_INTERVAL | Cleanup interval | 60s |
 
+## Testing
+
+```bash
+go test ./src/...
+```
+
 ## Graceful shutdown
 
 ```bash