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>

frontend/src/lib/portLinks.ts

@@ -0,0 +1,32 @@
+const WILDCARD_IPS = new Set(["", "0.0.0.0", "::"]);
+
+/** IPv6 literals need brackets in a URL; location.hostname already has them. */
+export function urlHost(host: string): string {
+  return host.includes(":") && !host.startsWith("[") ? `[${host}]` : host;
+}
+
+function isIpLiteral(host: string): boolean {
+  return /^\d{1,3}(\.\d{1,3}){3}$/.test(host) || host.startsWith("[");
+}
+
+/** Where a port bound to all interfaces is reached. The page's own hostname
+ *  only works when it *is* the Docker host — behind a reverse proxy it is the
+ *  proxy's domain, and domain:8080 lands on the proxy. So: the configured
+ *  host, else the page's hostname when that is an IP (or localhost), else the
+ *  host address the backend detected, else the page's hostname after all. */
+export function defaultLinkHost(
+  page: string,
+  settings?: { port_link_host: string; detected_host_ip: string | null }
+): string {
+  if (settings?.port_link_host) return settings.port_link_host;
+  if (isIpLiteral(page) || page === "localhost") return page;
+  return settings?.detected_host_ip || page;
+}
+
+/** Pick the host to link to: an explicit override, the bound
+ *  host IP if it's a concrete address, otherwise the default above. */
+export function linkHost(hostIp: string | undefined, fallback: string, override?: string): string {
+  if (override) return override;
+  if (hostIp && !WILDCARD_IPS.has(hostIp)) return hostIp;
+  return fallback;
+}