Refactor: Frontend-Fundament — Format-Utils, Dialog-Ref, Typen (Phase 3a)

- Neuer lib/format.ts: gb/fmtBytes/fmtSize/fmtEta/fmtCtx zentral; aus
  DashboardView/SystemView/ModelsView entdoppelt und importiert.
- CustomDialog: document.getElementById -> useRef (kein DOM-Query, robuster).
- api.ts: GitInfo/ComponentVersion/Versions typisiert, SystemStatus.versions
  ergänzt; App.tsx nutzt SystemStatus statt any.

tsc grün, Build grün, Dashboard verifiziert (keine Konsolenfehler, Formatierer
rendern identisch).

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

frontend/src/App.tsx

@@ -11,14 +11,14 @@ import { AgentView } from "@/views/AgentView"
 import { GuideView } from "@/views/GuideView"
 import { Placeholder } from "@/views/Placeholder"
 import { SystemDrawer } from "@/components/SystemDrawer"
-import { api, type Health } from "@/lib/api"
+import { api, type Health, type SystemStatus } from "@/lib/api"
 import { cn } from "@/lib/utils"
 
 export default function App() {
   const [view, setView] = useState<ViewId>("dashboard")
   const [health, setHealth] = useState<Health | null>(null)
   const [sidebarCollapsed, setSidebarCollapsed] = useState(() => localStorage.getItem("mc_sidebar_collapsed") === "true")
-  const [sysStatus, setSysStatus] = useState<any | null>(null)
+  const [sysStatus, setSysStatus] = useState<SystemStatus | null>(null)
   const [drawerOpen, setDrawerOpen] = useState(false)
   const [drawerTab, setDrawerTab] = useState<"maintenance" | "logs">("maintenance")
 
@@ -30,7 +30,7 @@ export default function App() {
   }, [])
 
   useEffect(() => {
-    const loadSys = () => api<any>("/api/system/status").then(setSysStatus).catch(() => {})
+    const loadSys = () => api<SystemStatus>("/api/system/status").then(setSysStatus).catch(() => {})
     loadSys()
     const t = setInterval(loadSys, 20000)
     return () => clearInterval(t)