feat: Günther-Agent (Netzer-Style) + Expertenblick im TipModal

- AgentChat-Widget mit SSE-Streaming, Quick-Actions, Multiple-Choice
- /api/agent/chat + /api/agent/insight Routen
- Expertenblick-Panel im TipModal (lazy load)
- Günther-Icon

backend/src/index.ts

@@ -15,6 +15,7 @@ import leaderboardRouter from './routes/leaderboard';
 import adminRouter from './routes/admin';
 import profileRouter from './routes/profile';
 import devRouter from './routes/dev';
+import agentRouter from './routes/agent';
 
 const app = express();
 const PORT = parseInt(process.env.PORT ?? '3001');
@@ -86,6 +87,16 @@ app.use(
   })
 );
 
+// Rate limit für Agent-Chat (Claude API Calls sind kostenpflichtig)
+app.use(
+  '/api/agent',
+  rateLimit({
+    windowMs: 60 * 1000, // 1 Minute
+    max: 10,             // 10 Chat-Nachrichten pro User/Minute
+    message: { error: 'Too many agent requests, bitte kurz warten.' },
+  })
+);
+
 // ============================================================
 // Health Check (ohne Auth – für Railway/Render/Uptime-Monitoring)
 // ============================================================
@@ -119,6 +130,7 @@ app.use('/api/tips', tipsRouter);
 app.use('/api/leaderboard', leaderboardRouter);
 app.use('/api/admin', adminRouter);
 app.use('/api/profile', profileRouter);
+app.use('/api/agent', agentRouter);
 if (process.env.NODE_ENV === 'development') {
   app.use('/api/dev', devRouter);
 }