Add FTP credentials management and UI enhancements

- Implement migration script to add ftp_username and ftp_password columns to nl43_config table.
- Create set_ftp_credentials.py script for updating FTP credentials in the database.
- Update requirements.txt to include aioftp for FTP functionality.
- Enhance index.html with FTP controls including enable, disable, check status, and list files features.
- Add JavaScript functions for handling FTP operations and displaying file lists.

app/main.py

@@ -73,7 +73,7 @@ async def health_devices():
         configs = db.query(NL43Config).filter_by(tcp_enabled=True).all()
 
         for cfg in configs:
-            client = NL43Client(cfg.host, cfg.tcp_port, timeout=2.0)
+            client = NL43Client(cfg.host, cfg.tcp_port, timeout=2.0, ftp_username=cfg.ftp_username, ftp_password=cfg.ftp_password)
             status = {
                 "unit_id": cfg.unit_id,
                 "host": cfg.host,