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.

docs/2-handbook/agents/web-page.md

@@ -81,14 +81,11 @@ at a given viewport width. Two columns:
   - **Links badge** (`🔗`): opens a popover listing `↑ dashboard`
     (back-link to the host dashboard, `${dashboardBase}`)
     followed by this agent's `agent_links()`-sourced navigation (stats,
-    screen when VNC is enabled, forge profile + config-repo mirror when
-    the agent has a forge account, any `services.hyperhive.agent.dashboardLinks`
+    screen when VNC is enabled, any `services.hyperhive.agent.dashboardLinks`
     extras) — all as real `<a>` elements, not a `Dropdown`-style
     command list, so ctrl/middle-click and "copy link address" keep
     working. Each `AgentLink.kind` resolves differently: `container` →
-    same-origin path; `forge` → `state.forge_public_url + url`, and
-    hive-agent drops the link entirely when that's unset (never guessed from
-    `<host>:3000`); `external` → already absolute. Same source
+    same-origin path; `external` → already absolute. Same source
     (`GET /api/state`'s `links` field) also feeds
     `DashboardState.links` for the dashboard card's icon strip —
     `agent_links()` in hive-agent is the single source of truth for