Link port chips to the Docker host, not the proxy's domain (0.67.3)

Ports published on 0.0.0.0 were linked at window.location.hostname. Opened
through a reverse proxy such as Nginx Proxy Manager that is the proxy's
domain, and domain:8080 ended up at the proxy instead of the container.

The backend now reads the host's address from the host's routing table
(${HOST_PROC_PATH}/1/net/route + fib_trie, the /proc mount the compose file
already has): the IPv4 address on the interface with the best default
route. There is no fallback to /proc/net, which in a bridged container is
the container's own namespace with an unreachable 172.x address.

The links use, in order: the new "Host address for port links" setting
(Settings -> General), the page's hostname when it is an IP or localhost,
the detected address, and the page's hostname as a last resort. Ports
bound to one specific address still link there; IPv6 hosts are bracketed.
The setting is validated before anything is written, so a bad value no
longer leaves the interval half-saved in the same request.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/services/settings_service.py

@@ -11,6 +11,7 @@ from database import engine
 from models.setting import Setting
 
 KEY_UPDATE_INTERVAL = "update_check_interval_minutes"
+KEY_PORT_LINK_HOST = "port_link_host"
 
 
 def get(session: Session, key: str, default: Any = None) -> Any:
@@ -43,3 +44,9 @@ def get_update_interval(session: Optional[Session] = None) -> int:
     if isinstance(val, int) and val > 0:
         return val
     return env_settings.UPDATE_CHECK_INTERVAL_MINUTES
+
+
+def get_port_link_host(session: Session) -> str:
+    """Host that port links point at, as configured; "" means detect it."""
+    val = get(session, KEY_PORT_LINK_HOST)
+    return val if isinstance(val, str) else ""