feat(web-ui): Remote Updates dashboard page — push code to workers from the UI

React component for /swarm-updates: per-host table polled every 10s,
row actions for Push Update / Update Updater / Rollback, a fleet-wide
'Push to All' modal with the include_self toggle, and toast feedback
per result.

Admin-only (both server-gated and UI-gated). Unreachable hosts surface
as an explicit state; actions are disabled on them. Rollback is
disabled when the worker has no previous release slot (previous_sha
null from /hosts).

decnet_web/src/App.tsx

@@ -9,6 +9,7 @@ import Attackers from './components/Attackers';
 import AttackerDetail from './components/AttackerDetail';
 import Config from './components/Config';
 import Bounty from './components/Bounty';
+import RemoteUpdates from './components/RemoteUpdates';
 
 function isTokenValid(token: string): boolean {
   try {
@@ -64,6 +65,7 @@ function App() {
           <Route path="/attackers" element={<Attackers />} />
           <Route path="/attackers/:id" element={<AttackerDetail />} />
           <Route path="/config" element={<Config />} />
+          <Route path="/swarm-updates" element={<RemoteUpdates />} />
           <Route path="*" element={<Navigate to="/" replace />} />
         </Routes>
       </Layout>