docs(web-ui/agent): fix stale NavLink type name

Verified against hive-agent/src/web_ui/state.rs: the struct is AgentLink
(AgentLinkKind for kind), not NavLink -- NavLink doesn't exist anywhere in
the Rust or frontend source.

docs/web-ui/agent.md

@@ -36,7 +36,7 @@ through. Three flex columns:
     also appears in `DashboardState.links` (`GET /api/dashboard-state`)
     for the dashboard card's icon strip. Both are produced by
     `agent_links()` in hive-ag3nt — the single source of truth.
-    Each `NavLink.kind` resolves
+    Each `AgentLink.kind` resolves
     differently in the frontend: `Container` → same-origin path
     (the agent page is itself container-local); `Forge` →
     `state.forge_public_url + url` (sourced from