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/models/setting.py

@@ -80,6 +80,9 @@ class WebhookRead(SQLModel):
 
 class SettingsRead(SQLModel):
     update_check_interval_minutes: int
+    # Where links to published ports point. "" = not set, use detected_host_ip.
+    port_link_host: str
+    detected_host_ip: Optional[str]
     env_webhook_count: int
     available_events: list[str]
     webhook_types: list[str]
@@ -87,3 +90,5 @@ class SettingsRead(SQLModel):
 
 class SettingsUpdate(SQLModel):
     update_check_interval_minutes: Optional[int] = None
+    # "" clears it back to the detected address.
+    port_link_host: Optional[str] = None