refactor(scanner): make poll interval dynamic from database

- Add GetPollInterval() method to MediaScanner to read from database
- Add GetAutoScanEnabled() method to check if auto-scan is enabled
- Remove ScanPollIntervalSeconds from config (now DB-driven)
- Update NewMediaScanner signature to not require interval parameter
- Remove SCAN_POLL_INTERVAL_SECONDS from docker-compose env var

docker-compose.yml

@@ -10,7 +10,6 @@ services:
       POSTGRES_USER: postgres
       POSTGRES_PASSWORD: ${DBPASS}
       COOKIE_SECURE: false # make true in production with HTTPS
-      SCAN_POLL_INTERVAL_SECONDS: 30
     volumes:
       - postgres_data:/var/lib/postgresql/data
       - ./database/schema:/docker-entrypoint-initdb.d