feat: run.sh restart/stop/status + real DB connector + GitLab CI

1. run.sh: start/stop/restart/status/logs/build/test
   - PID file management in .pids/
   - Colored output, health check wait, log files
   - Auto alembic migrate on start

2. DB Connector (replaces mock aiomysql):
   - MySQL: aiomysql (connect/query/dml/test)
   - PostgreSQL: asyncpg (connect/query/dml/test)
   - SQLite: sqlite3 via executor (connect/query/dml/test)
   - Unified interface: DBConnector.test_connection/execute_query/execute_dml
   - Connection test returns version + latency

3. GitLab CI/CD pipeline:
   - test: backend pytest + frontend build
   - build: Docker images (manual trigger)
   - deploy: SSH deploy (manual trigger)
   - Cache: pip + node_modules

Tests: 128 passing, frontend build: OK

backend/requirements.txt

@@ -10,3 +10,5 @@ python-multipart>=0.0.6
 cryptography>=41.0.0
 sqlparse>=0.4.4
 alembic>=1.13.0
+aiomysql>=0.2.0
+asyncpg>=0.29.0