Frontend: globale Error Boundary (Review F4) + dist-Rebuild

JS-Fehler in einer View fuehrten zum weissen Screen ohne Meldung; jetzt Fehleranzeige
mit Neu-laden-Knopf am App-Root (GraphView behaelt seine eigene Boundary).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/main.tsx

@@ -2,6 +2,7 @@ import React from "react"
 import ReactDOM from "react-dom/client"
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query"
 import App from "./App"
+import { AppErrorBoundary } from "./components/AppErrorBoundary"
 import "./index.css"
 
 // Zentraler Daten-Layer: Caching, Dedup, Retry, Polling pro Query-Hook.
@@ -17,8 +18,10 @@ const queryClient = new QueryClient({
 
 ReactDOM.createRoot(document.getElementById("root")!).render(
   <React.StrictMode>
-    <QueryClientProvider client={queryClient}>
-      <App />
-    </QueryClientProvider>
+    <AppErrorBoundary>
+      <QueryClientProvider client={queryClient}>
+        <App />
+      </QueryClientProvider>
+    </AppErrorBoundary>
   </React.StrictMode>,
 )