USWDS-Elements: restructure tokens into tier-first directory layout (system/theme/state)

[ethangardner]

Summary

Migrates the token source from a flat category-first layout (tokens/{colors,spacing,breakpoints}/) to a tier-first layout. Updates the Style Dictionary config and build helpers to match. No token values change; no published token names change. This does more closely match the documented convention from USWDS' documentation where we have system, theme, and state tokens.

Problem

USWDS's color model has three named layers: system (raw palette), theme (branding roles), and state (feedback roles). The previous flat structure of our tokens didn't reflect this

Solution

The tier-first structure aligns the source layout with USWDS's own published vocabulary and is the prerequisite for all subsequent token work. Other tokens implicitly use the system, theme, state convention as well, even if it is not named as such in the documentation. For example, $theme-modal-lg-max-width is the semantic (theme) alias for the tablet-lg system unit token: https://designsystem.digital.gov/documentation/settings/#configuring-settings-maps.

Major changes

Token source files (moves only, no content changes)

• tokens/colors/*.json (28 files) → tokens/system/color/*.json
• tokens/spacing/spacing.json → tokens/system/spacing/spacing.json
• tokens/breakpoints/breakpoints.json → tokens/system/breakpoints/breakpoints.json
• Old directories removed
• Helpers and style dictionary updates and tests

Testing

npm run build:tokens   # exits 0; 6 output files generated
npm run test:ci        # 49 tests, 6 files — all pass

Token name identity check:

grep "usa-color-blue-5:" build/css/system/color.css
# → --usa-color-blue-5: #eff6fb;  (identical to pre-restructure)

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