fix(#888): use gateway forge URL in dashboard links

Dashboard links to the forge were hardcoded as http://<hostname>:3000,
which breaks when the operator accesses the dashboard through
hive-gateway (forge is served at forge.<domain> with no port).

- nix/modules/hive-c0re.nix: inject HIVE_FORGE_PUBLIC_URL when
  forge.behindGateway = true (e.g. http://forge.pr1ma.darkest.space)
- hive-c0re/src/dashboard.rs: expose forge_url: Option<String> in
  StateSnapshot, reading from HIVE_FORGE_PUBLIC_URL
- frontend/packages/dashboard/src/tabs.js: use state.forge_url when
  present; fall back to http://<hostname>:3000 for gateway-off /
  local-dev deploys

frontend/packages/dashboard/src/tabs.js

@@ -580,7 +580,11 @@ window.marked = marked;
       // and must never reach the HTML parser.
       const navStrip = el('span', { class: 'nav-strip' });
       head.append(navStrip);
-      const forgeBase = `http://${hostname}:3000`;
+      // Forge public URL: prefer state.forge_public_url (set by the NixOS
+      // module when forge.behindGateway=true, e.g.
+      // "https://forge.pr1ma.darkest.space"), fall back to
+      // "<hostname>:3000" for gateway-off / local-dev deploys.
+      const forgeBase = (s && s.forge_public_url) || `http://${hostname}:3000`;
       // Container nav-strip links resolve against the same base as the
       // primary `name` link — gateway-prefixed when the gateway is in
       // front, direct TCP otherwise. Strips the trailing slash so
@@ -1786,7 +1790,11 @@ window.marked = marked;
     // forge link base — only when the hive-forge container is up.
     const fs = window.__hyperhive_state;
     const hostname = (fs && fs.hostname) || window.location.hostname;
-    const forgeBase = (fs && fs.forge_present) ? `http://${hostname}:3000` : null;
+    // Prefer state.forge_public_url (set when forge.behindGateway=true,
+    // e.g. "https://forge.pr1ma.darkest.space") over the direct :3000 port.
+    const forgeBase = (fs && fs.forge_present)
+      ? (fs.forge_public_url || `http://${hostname}:3000`)
+      : null;
 
     const ul = el('ul', { class: 'approvals' });
     for (const a of pending) {