feat: Support "bold", "normal" in font weight.

[divyanshub024]

Description:

Currently, the fontWeight property expects numeric values like "w400" or "w700". However, it’s common for designers and developers to use human-readable strings such as "normal" and "bold".

This feature request proposes:
• Support for "normal" → mapped to "w400"
• Support for "bold" → mapped to "w700"

This will make Stac JSONs more readable and accessible, especially for non-technical users or config-based UIs.