feat: Notifications page, Sidebar layout fixes, and Achievements enhancements

- implemented /notifications page with overdue/upcoming alerts
- Fixed sidebar scrolling in collapsed mode
- Moved notification button to sidebar footer
- Enhanced Achievements page with streak stats and tooltips
- Improved XP history to show task titles
- Added missing translations (en/de)
- Removed top bar header
- Fixed Docker environment routing

server/index.ts

@@ -42,6 +42,13 @@ app.use((req, res, next) => {
     }
   });
 
+  // Ensure no caching for API routes to prevent sticky sessions
+  if (path.startsWith("/api")) {
+    res.header('Cache-Control', 'no-store, no-cache, must-revalidate, proxy-revalidate');
+    res.header('Pragma', 'no-cache');
+    res.header('Expires', '0');
+  }
+
   next();
 });