Add Custom CSS Section to Status Page

[mohicody]

Description: Implement a custom CSS section in the Status Page creation interface to allow users to add custom styling to their status pages.

Requirements:

1. Add a new "Custom CSS" section to the Status Page Settings tab after the appearance section
2. Implement a simple code editor with CSS syntax highlighting only
3. Update the StatusPage model/schema to include a customCSS field (string type)
4. Add validation and sanitization for the CSS input to prevent XSS attacks
5. Update the API endpoints and rendering logic to handle and apply the custom CSS