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/components/AppErrorBoundary.tsx

@@ -0,0 +1,38 @@
+import React from "react"
+
+// Globale Error Boundary (Review F4): Ein JS-Fehler in einer View riss vorher die komplette
+// App in einen weißen Screen. Hier: Fehler anzeigen + Neu-laden-Knopf, Rest bleibt bedienbar
+// nach Reload. (GraphView hat zusätzlich seine eigene Boundary für Three.js-Crashes.)
+interface State { error: Error | null }
+
+export class AppErrorBoundary extends React.Component<React.PropsWithChildren, State> {
+  state: State = { error: null }
+
+  static getDerivedStateFromError(error: Error): State {
+    return { error }
+  }
+
+  componentDidCatch(error: Error, info: React.ErrorInfo) {
+    console.error("Unbehandelter UI-Fehler:", error, info.componentStack)
+  }
+
+  render() {
+    if (!this.state.error) return this.props.children
+    return (
+      <div className="min-h-screen flex items-center justify-center bg-neutral-950 text-neutral-200 p-8">
+        <div className="max-w-lg space-y-4 text-center">
+          <div className="text-2xl">Da ist etwas schiefgelaufen.</div>
+          <div className="text-sm text-neutral-400 break-all">
+            {this.state.error.message}
+          </div>
+          <button
+            className="px-4 py-2 rounded-lg bg-neutral-800 hover:bg-neutral-700 border border-neutral-700"
+            onClick={() => window.location.reload()}
+          >
+            Neu laden
+          </button>
+        </div>
+      </div>
+    )
+  }
+}

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>,
 )