Extend ensure_utf8_encoding() to support both internal and external PostgreSQL.
- Modular mode: Uses TCP connection with PGPASSWORD authentication
- AIO mode: Uses Unix socket as postgres user
- Explicitly set database owner during recreation (fixes missing --owner flag)
- Conversion logic (dump/drop/recreate/restore) works for both AIO and modular modes
- Skip internal PostgreSQL setup entirely when DISPATCHARR_ENV=modular