Feature: Signal forms for metadata

[HeyItsBATMAN]

With Angular 21 being released, we now have access to Signal Forms, which is their next step of form-development based on the Signal API.

This is as good of a timing as ever to update the metadata form for 1. reactivity and 2. helpful error messages.

Here is my plan of work:

• Create test branch with update to Angular 21
• Test out signal based forms for metadata
• Evaluate if all features work as desired