feat(spec): add textTransform typography token

[edgarasben]

Summary

Adds textTransform as an optional typography token property.

This enables DESIGN.md files to express text casing rules, such as uppercase labels, in a machine-readable way instead of relying only on prose.

Motivation

Text casing is currently only expressible through natural language, for example:

Labels should be uppercase.

That works for humans, but it is harder for tooling and agents to interpret consistently. Adding textTransform lets a design system define casing behavior directly in typography tokens.

Example

typography:
 caps:
   fontFamily: Inter
   fontSize: 12px
   textTransform: uppercase

Changes

• Adds textTransform to the typography token spec
• Updates the generated spec documentation
• Updates the README typography token reference
• Adds model support for reading textTransform
• Adds a model test covering textTransform

Compatibility

This is optional and backward-compatible. Existing DESIGN.md files do not need to change.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[edgarasben]

Looks like my CLA is failing, no idea why.