remove the forge links from the hive dashboard and the agent page

Each agent row on the hive dashboard, and the agent page's link menu, linked
to the agent's forge profile and its config repo. Both are gone, with what
only they used:

- hive-agent no longer builds the two links, the `Forge` link kind, or the
  `forge_public_url` field of its state, and no longer reads
  `HIVE_FORGE_PUBLIC_URL`. The agent page's link menu and the dashboard row's
  icon strip (which skips a forge link an agent not yet rebuilt still sends)
  drop their forge handling.
- hive-c0re's dashboard state no longer carries `forge_public_url`.
- `HIVE_FORGE_PUBLIC_URL` is no longer forwarded to agents through the meta
  flake (the forwarded-variable list, its test fixture, the controller's
  settings and the VM test), so the next meta flake render differs by that
  one line. hive-c0re still reads it for the forge URL a hive publishes, so
  `swarm.forge.publicUrl` stays, with its description corrected.
- The docs stop describing the links.

nix/host-modules/hive-forge/service.nix

@@ -78,17 +78,11 @@ in
       defaultText = lib.literalExpression ''"https://''${domain}"'';
       example = "https://forge.example.com";
       description = ''
-        Browser-facing forge URL the dashboard uses to build clickable
-        forge links (the per-agent-row forge links) —
-        sourced into every agent container + hive-c0re as
-        `HIVE_FORGE_PUBLIC_URL`.
+        Browser-facing forge URL, sourced into hive-c0re as
+        `HIVE_FORGE_PUBLIC_URL` and published with the hive's URLs.
 
         Defaults to `https://''${cfg.domain}`, the gateway vhost. When
-        `null`, the dashboard **hides** forge links rather than
-        guessing one — see `docs/2-handbook/hives/dashboard.md::Container row` for
-        the rationale (a link built from the operator's own browser
-        hostname + a container port is only an accident away from
-        wrong on any deployment that isn't plain localhost).
+        `null`, the hive publishes no forge URL rather than guessing one.
       '';
     };
 

nix/host-modules/swarm-controller.nix

@@ -267,9 +267,6 @@ let
       vars = {
         HIVE_FORGE_URL = "http://${forgeCfg.domain}";
       }
-      // lib.optionalAttrs (forgeCfg.publicUrl != null) {
-        HIVE_FORGE_PUBLIC_URL = forgeCfg.publicUrl;
-      }
       // lib.optionalAttrs (matrixCfg.gatewayHost != null) {
         HIVE_MATRIX_URL = "http://${matrixCfg.gatewayHost}";
       }

nix/vm-tests/full-setup.nix

@@ -49,7 +49,6 @@ let
     "HIVE_AGENT_BAO_SERVICES_PKI_MOUNT"
     "HIVE_AGENT_LOGS_QUERY_URL"
     "HIVE_AGENT_METRICS_URL"
-    "HIVE_FORGE_PUBLIC_URL"
     "HIVE_FORGE_URL"
     "HIVE_MATRIX_URL"
   ];