feat: name database file after device name for multi-device support

Database file is now named {device_name}.db (e.g. MarWoj.db) instead of
the generic mc-webui.db. On first boot, mc-webui.db is automatically
renamed once the device name is detected. On subsequent boots, the
existing device-named DB is found by scanning the config directory.

This enables future multi-device support where each MeshCore device
has its own separate database file.

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

docker-compose.yml

@@ -18,7 +18,6 @@ services:
       - MC_SERIAL_PORT=${MC_SERIAL_PORT:-auto}
       - MC_DEVICE_NAME=${MC_DEVICE_NAME:-MeshCore}
       - MC_CONFIG_DIR=/data
-      - MC_DB_PATH=/data/mc-webui.db
       - MC_TCP_HOST=${MC_TCP_HOST:-}
       - MC_TCP_PORT=${MC_TCP_PORT:-5555}
       - MC_BACKUP_ENABLED=${MC_BACKUP_ENABLED:-true}