Add Overview page with kind-grouped node cards and RAM/disk metrics.

Batch-fetch action widgets so the dashboard can show free/total memory and disk usage without N+1 requests.

webui/src/App.tsx

@@ -1,4 +1,5 @@
 import { useEffect, useState, type FormEvent } from 'react'
+import { OverviewPanel } from './OverviewPanel'
 import {
   beginMyTOTP,
   changeMyPassword,
@@ -4388,6 +4389,8 @@ function App() {
               setSidebarCountsRefreshToken((token) => token + 1)
             }}
           />
+        ) : activeSection === 'overview' ? (
+          <OverviewPanel />
         ) : (
           <p>Coming soon</p>
         )}