dashboard: serve the dashboard at /, fold kept state in as a tab, add a pages menu

Drop the H0M3 tile hub and the core page. The dashboard is now the index;
kept state is its fifth tab. A pages menu in the chrome links flow, stats,
API docs and the swarm UI. The swarm apex URL comes from
services.hyperhive.swarm.domain via HIVE_SWARM_PUBLIC_URL and the new
swarm_public_url field of the state snapshot.

docs/web-ui/agent.md

@@ -71,7 +71,7 @@ at a given viewport width. Two columns:
   - **Inbox / todos pills** (`📬 inbox · N` / `📋 todos · N`): hidden
     when empty; selecting it opens the matching flyout in the side panel.
   - **Links badge** (`🔗`): opens a popover listing `↑ dashboard`
-    (back-link to the host dashboard, `${dashboardBase}dashboard.html`)
+    (back-link to the host dashboard, `${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`