feat(shop): implement CSRF protection and improve UI/UX

- Add CSRF token validation to the shop purchase process to prevent cross-site request forgery.
- Implement a unique constraint on `UserShopItem` to prevent duplicate purchases of the same item.
- Refactor the shop template with a modern, responsive grid layout and improved visual feedback for owned items.
- Enhance CSS with better dark/light mode support, including improved navbar styling and scrollbar customization.
- Add `.env_example` and update documentation for environment variable setup.
- Integrate `python-dotenv` for environment variable management.
- Improve logging configuration for the application.
- Update `.gitignore` to include `venv/` and `.env`.

Co-authored-by: Copilot <copilot@github.com>

.gitignore

@@ -10,11 +10,10 @@ migrations
 *.env
 .vscode
 routes/__pycache__
-tools
 *.pot
 *.mo
 routes/oauth.py
 static/profile_pics
 static/uploads
-commands.txt
-py-to-exemfc.json
+venv/
+.env