feat: integrate AI grading functionality

- Added OpenAI package to backend dependencies for AI grading.
- Implemented new grading routes and services to handle AI grading requests.
- Updated admin settings to include AI provider configuration options.
- Enhanced frontend components to support AI grading, including UI for testing AI connection and displaying AI feedback.
- Updated results component to allow for AI-assisted grading and display of suggested grades.
- Added internationalization support for new AI grading features in both English and Dutch.

backend/package.json

@@ -19,6 +19,7 @@
     "helmet": "^8.1.0",
     "jsonwebtoken": "^9.0.2",
     "nodemailer": "^7.0.3",
+    "openai": "^4.95.0",
     "zod": "^3.24.2"
   },
   "devDependencies": {