Refactor font family handling from URLs to variable names

[coderabbitai]

Problem

Currently, the application accepts a full URL for font family configuration (via systemConfig.ui?.url) and then extracts the font family name from the URL. This approach is suboptimal and should be refactored.

Proposed Solution

Instead of accepting a full URL:

1. Accept a variable name for the font family
2. Construct the appropriate URL on the backend/server side

Scope

This change will need to be implemented in:

• The main application code (src/app/layout.tsx and related utilities)
• The wizard/configuration tool that generates these configurations

Context

Raised in: #1625 (comment)

Requested by: @j-paterson