Add request and SQL performance logging features to backend

- Implement request timing middleware in app.js to log slow requests and all requests based on environment variables.
- Enhance sequelize.js with optional SQL query timing and logging capabilities, allowing for performance monitoring of database queries.

backend/app.js

@@ -1,6 +1,7 @@
 import express from 'express';
 import path from 'path';
 import { fileURLToPath } from 'url';
+import crypto from 'crypto';
 import chatRouter from './routers/chatRouter.js';
 import authRouter from './routers/authRouter.js';
 import navigationRouter from './routers/navigationRouter.js';
@@ -25,6 +26,25 @@ const __dirname = path.dirname(__filename);
 
 const app = express();
 
+// Request-Timing (aktivierbar per ENV)
+// - LOG_SLOW_REQ_MS=200: Logge Requests, die länger dauern als X ms (Default 500)
+// - LOG_ALL_REQ=1: Logge alle Requests
+const LOG_ALL_REQ = process.env.LOG_ALL_REQ === '1';
+const LOG_SLOW_REQ_MS = Number.parseInt(process.env.LOG_SLOW_REQ_MS || '500', 10);
+app.use((req, res, next) => {
+  const reqId = req.headers['x-request-id'] || (crypto.randomUUID ? crypto.randomUUID() : crypto.randomBytes(8).toString('hex'));
+  req.reqId = reqId;
+  res.setHeader('x-request-id', reqId);
+  const t0 = Date.now();
+  res.on('finish', () => {
+    const ms = Date.now() - t0;
+    if (LOG_ALL_REQ || ms >= LOG_SLOW_REQ_MS) {
+      console.log(`⏱️  REQ ${ms}ms ${res.statusCode} ${req.method} ${req.originalUrl} rid=${reqId}`);
+    }
+  });
+  next();
+});
+
 const corsOptions = {
   origin: ['http://localhost:3000', 'http://localhost:5173', 'http://127.0.0.1:3000', 'http://127.0.0.1:5173'], 
   methods: ['GET', 'HEAD', 'PUT', 'PATCH', 'POST', 'DELETE'],