[Feature request] Create a sample Figma file as a community reference

### Description

New users of the Annotation Toolkit would benefit from seeing real examples of how annotations are applied to actual design mockups. A sample Figma file that demonstrates the toolkit in use would serve as a practical learning resource.

### Requested change

Create a companion Figma community file that shows annotated mockups, demonstrating how to use various annotation types in context.
Open questions

- Should the sample file use GitHub UI as the subject, or something more generic that any team could relate to?
- Should it aim to cover all annotation component types, or focus on the most common ones? If a subset, which ones would be most helpful to showcase first?

### Why

Seeing annotations applied in context is one of the most effective ways to learn how to use them. A reference file would lower the barrier to entry for new users and give teams a starting point they can reference when annotating their own work.

Start by resolving the open questions about the mockup subject and which annotation component types to cover. Create and publish a companion Figma community file with annotated mockups that demonstrates the toolkit in context; the work is done when it provides a usable reference for new users.

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