refactor: migrate data storage from JSON/map files to SQLite

Replace servers.json, certificates.json, and map file parsing with
SQLite (WAL mode) as single source of truth. HAProxy map files are
now generated from SQLite via sync_map_files().

Key changes:
- Add db.py with schema, connection management, and JSON migration
- Add DB_FILE config constant
- Delegate file_ops.py functions to db.py
- Refactor domains.py to use file_ops instead of direct list manipulation
- Fix subprocess.TimeoutExpired not caught (doesn't inherit TimeoutError)
- Add DB health check in health.py
- Init DB on startup in server.py and __main__.py
- Update all 359 tests to use SQLite-backed functions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

haproxy_mcp/config.py

@@ -31,6 +31,7 @@ WILDCARDS_MAP_FILE: str = os.getenv("HAPROXY_WILDCARDS_MAP_FILE", "/opt/haproxy/
 WILDCARDS_MAP_FILE_CONTAINER: str = os.getenv("HAPROXY_WILDCARDS_MAP_FILE_CONTAINER", "/usr/local/etc/haproxy/wildcards.map")
 SERVERS_FILE: str = os.getenv("HAPROXY_SERVERS_FILE", "/opt/haproxy/conf/servers.json")
 CERTS_FILE: str = os.getenv("HAPROXY_CERTS_FILE", "/opt/haproxy/conf/certificates.json")
+DB_FILE: str = os.getenv("HAPROXY_DB_FILE", "/opt/haproxy/conf/haproxy_mcp.db")
 
 # Certificate paths
 CERTS_DIR: str = os.getenv("HAPROXY_CERTS_DIR", "/opt/haproxy/certs")