swarm-ui: agent roster page with per-agent config-PR status

New AgentsPage at /agents: fetches GET /api/agents (roster names) and
GET /api/config-prs (bulk config-PR status) and merges them into one
table, one row per agent. Reuses the existing Panel/Table/StatusChip/
RefreshIntervalPicker components exactly as HivesPage does — the roster
page and the config-PR panel turned out to be the same page rather than
two separate pieces of UI.

Adds a nav entry (green accent, the next unused base16 chromatic slot)
between hives and new agent.

frontend/packages/swarm-ui/src/App.tsx

@@ -2,6 +2,7 @@
 // page component under `./pages/`; this file just maps paths to them.
 import { Route, Switch } from 'wouter-preact';
 import { Shell } from './shell/Shell.js';
+import { AgentsPage } from './pages/AgentsPage.js';
 import { ComponentsPage } from './pages/ComponentsPage.js';
 import { CreateAgentPage } from './pages/CreateAgentPage.js';
 import { JobsPage } from './pages/JobsPage.js';
@@ -21,6 +22,7 @@ export function App() {
     <Shell>
       <Switch>
         <Route path="/" component={HivesPage} />
+        <Route path="/agents" component={AgentsPage} />
         <Route path="/create-agent" component={CreateAgentPage} />
         <Route path="/jobs" component={JobsPage} />
         <Route path="/components" component={ComponentsPage} />