Phase 3: ddns_manager — DDNS client, provider adapters, IP heartbeat

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

api/app.py

@@ -42,6 +42,7 @@ from managers import (
     routing_manager, vault_manager, container_manager,
     cell_link_manager, auth_manager, setup_manager,
     caddy_manager,
+    ddns_manager,
     firewall_manager, EventType,
 )
 # Re-exports: tests do `from app import CellManager` and `from app import _resolve_peer_dns`
@@ -578,6 +579,9 @@ def health_monitor_loop():
 health_monitor_thread = threading.Thread(target=health_monitor_loop, daemon=True)
 health_monitor_thread.start()
 
+# Start DDNS heartbeat thread (updates public IP every 5 minutes when a provider is configured)
+ddns_manager.start_heartbeat()
+
 def _local_subnets():
     """Return all subnets the container is directly connected to (from routing table)."""
     import ipaddress as _ipa, socket as _sock, struct as _struct