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/tools/health.py

@@ -10,6 +10,7 @@ from pydantic import Field
 from ..config import (
     MAP_FILE,
     SERVERS_FILE,
+    DB_FILE,
     HAPROXY_CONTAINER,
 )
 from ..exceptions import HaproxyError
@@ -88,7 +89,7 @@ def register_health_tools(mcp):
         # Check configuration files
         files_ok = True
         file_status: dict[str, str] = {}
-        for name, path in [("map_file", MAP_FILE), ("servers_file", SERVERS_FILE)]:
+        for name, path in [("map_file", MAP_FILE), ("db_file", DB_FILE)]:
             exists = remote_file_exists(path) if REMOTE_MODE else __import__('os').path.exists(path)
             if exists:
                 file_status[name] = "ok"