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/haproxy_client.py

@@ -2,6 +2,7 @@
 
 import socket
 import select
+import subprocess
 import time
 
 from .config import (
@@ -161,7 +162,7 @@ def reload_haproxy() -> tuple[bool, str]:
         if result.returncode != 0:
             return False, f"Reload failed: {result.stderr}"
         return True, "OK"
-    except TimeoutError:
+    except (TimeoutError, subprocess.TimeoutExpired):
         return False, f"Command timed out after {SUBPROCESS_TIMEOUT} seconds"
     except FileNotFoundError:
         return False, "ssh/podman command not found"