feat: add dark mode, navigation, and Web Vitals tracking to marketplace

Backend:
- Simplify DatabaseConfig: remove effective_url property and project root finder
- Update to Pydantic v2 model_config (replace nested Config class)
- Add web_vitals router to main.py and __init__.py
- Fix ExplorerService datetime handling (ensure timezone-naive comparisons)
- Fix status_label extraction to handle both enum and string job states

Frontend (Marketplace):
- Add dark mode toggle with system preference detection

website/docs/marketplace-web.html

@@ -260,7 +260,7 @@ docker run -d \
                 <ul>
                     <li>Check the <a href="full-documentation.html">issue tracker</a></li>
                     <li>Join our <a href="https://discord.gg/aitbc">Discord</a></li>
-                    <li>Contact: <a href="mailto:aitbc@bubuit.net">aitbc@bubuit.net</a></li>
+                    <li>Contact: <a href="mailto:andreas.fleckl@bubuit.net">andreas.fleckl@bubuit.net</a></li>
                 </ul>
             </section>
         </div>