Validate Label 3 Strong (10px/600) in the Modern UI type system

## Description

The Figma typography documentation defines Label 3 as 10px Regular (400). In the product, `--vscode-agents-fontSize-label3` is also paired with Semi Bold (600), effectively creating an undocumented **Label 3 Strong** style.

This issue is to validate whether Label 3 Strong is an intentional type role that should become part of the design system.

## Product examples

The 10px/600 combination currently appears on compact UI elements such as:

- Profile initials badges
- Review type and line labels
- Suggested-change labels
- Subagent confirmation counters
- Git status badges

## Validation needed

Please confirm whether these elements require a distinct **Label 3 Strong — 10px/600** role.

If the role is valid:

- Define its intended usage and boundaries.
- I will add Label 3 Strong to the Figma typography documentation.

If the role is not valid:

- Update the product uses to an existing documented type style.
- Keep Label 3 at its documented 10px/400 weight.

## Acceptance criteria

- A decision is documented on whether Label 3 Strong is part of the Modern UI type system.
- If approved, its semantic role and usage guidance are defined.
- If rejected, existing product uses are identified for alignment with a supported style.
- Product and Figma typography remain consistent.

Font ramp Figma [link](https://www.figma.com/design/nE50XAgPReJgrEDmC0aLPI/VS-Code-Design-Foundation-2026?node-id=122-1535&t=cV3egSRhDSuEp50o-1)