Refactor: TanStack-Query-Daten-Layer + useDialog (Phase 3b)

- @tanstack/react-query (v5) als zentraler Daten-Layer; QueryClientProvider
  in main.tsx (retry 1, kein refetchOnWindowFocus, staleTime 5s).
- lib/queries.ts: Domänen-Hooks (useHealth/useSystemStatus/useServices/
  useModels/useRouting/useJobs/useTokenStats/useAgentStatus/useUpdates/
  useDiscover/useConnect/useMemory) + zentrale Query-Keys (qk) + invalidate.
  Gleicher Key = eine Anfrage über alle Views (Dedup), einheitliches Polling.
- lib/useDialog.tsx: ein Hook für Alert/Confirm/Prompt statt 5x dupliziertem
  Dialog-State + showAlert/showConfirm.
- api.ts: TokenStats + ModelsResp typisiert.
- Migriert auf Hooks/useDialog: App, SystemView, AgentView, ConnectView,
  MemoryView (manuelles useEffect+setInterval entfernt; Mutationen
  invalidieren gezielt die Query-Keys).

Verifiziert: tsc grün, Build grün, alle migrierten Views ohne Konsolenfehler,
Live-Daten (CPU/RAM/Dienste) rendern korrekt.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package-lock.json

@@ -8,6 +8,7 @@
       "name": "mission-control-2-frontend",
       "version": "2.0.0",
       "dependencies": {
+        "@tanstack/react-query": "^5.101.1",
         "clsx": "^2.1.1",
         "cmdk": "^1.1.1",
         "lucide-react": "^0.460.0",
@@ -1810,6 +1811,32 @@
         "vite": "^5.2.0 || ^6 || ^7 || ^8"
       }
     },
+    "node_modules/@tanstack/query-core": {
+      "version": "5.101.1",
+      "resolved": "https://registry.npmjs.org/@tanstack/query-core/-/query-core-5.101.1.tgz",
+      "integrity": "sha512-Y6Y92dkXtNqx67m2pMSxUsA3zOCwv862JexZRP8/EPwvKXMPu9m8rv43spiXWzOUIggQ3SQApttALStzhA8B4g==",
+      "license": "MIT",
+      "funding": {
+        "type": "github",
+        "url": "https://github.com/sponsors/tannerlinsley"
+      }
+    },
+    "node_modules/@tanstack/react-query": {
+      "version": "5.101.1",
+      "resolved": "https://registry.npmjs.org/@tanstack/react-query/-/react-query-5.101.1.tgz",
+      "integrity": "sha512-ZnONUuQKJe1bJMStXUL1s5uKN9FcfC28j5cK+iDZcdSHtUv1wtin1cGc/Oewhf2Oc4eKY7lggtpvT/AbMmhHew==",
+      "license": "MIT",
+      "dependencies": {
+        "@tanstack/query-core": "5.101.1"
+      },
+      "funding": {
+        "type": "github",
+        "url": "https://github.com/sponsors/tannerlinsley"
+      },
+      "peerDependencies": {
+        "react": "^18 || ^19"
+      }
+    },
     "node_modules/@types/babel__core": {
       "version": "7.20.5",
       "resolved": "https://registry.npmjs.org/@types/babel__core/-/babel__core-7.20.5.tgz",