feat(admin): add full-chain trace and performance monitoring

- Backend: trace.Logger ring-buffer for request chain events
- Backend: perf.Monitor with runtime.MemStats sampling every 10s
- Backend: /api/v1/admin/trace and /api/v1/admin/perf endpoints
- Frontend: TracePage — timeline with hop icons and status dots
- Frontend: PerformancePage — memory/GC bar charts + live stats
- Admin nav expanded to 11 items

frontend/web/src/App.tsx

@@ -12,6 +12,8 @@ import LLMCallsPage from './pages/admin/LLMCallsPage'
 import SystemPage from './pages/admin/SystemPage'
 import ModelsPage from './pages/admin/ModelsPage'
 import BridgePage from './pages/admin/BridgePage'
+import TracePage from './pages/admin/TracePage'
+import PerformancePage from './pages/admin/PerformancePage'
 import LoginPage from './pages/LoginPage'
 
 export default function App() {
@@ -42,6 +44,8 @@ export default function App() {
           <Route path="llm-calls" element={<LLMCallsPage />} />
           <Route path="models" element={<ModelsPage />} />
           <Route path="bridge" element={<BridgePage />} />
+          <Route path="trace" element={<TracePage />} />
+          <Route path="perf" element={<PerformancePage />} />
           <Route path="system" element={<SystemPage />} />
         </Route>
       </Routes>