Add and use permission table, update CLI and README.md

src/ddns_service/cleanup.py

@@ -96,10 +96,14 @@ def cleanup_expired(app, start_time=None):
             continue
 
         try:
-            hostname.save()
+            if hostname.last_ipv4 is None and hostname.last_ipv6 is None:
+                hostname.delete_instance()
+            else:
+                hostname.save()
+
         except DatabaseError as e:
             logging.error(
-                f"DB save failed after retries: hostname={hostname.hostname} "
+                f"DB operation failed after retries: hostname={hostname.hostname} "
                 f"zone={hostname.zone}: {e}"
             )