feat: Adds color seed API and palette generation utilities

[jkuelz]

Issue #, if available:

Description of changes:

• Seed-based color palette generation

  • Added color-generation/ module with HCT (Hue-Chroma-Tone) color space utilities
  • Implemented palette generators for primary, neutral, and warning color schemes
  • Support for both single seed colors and mode-aware seeds (light/dark)
  • Automatic generation of 50-1000 palette steps from a single seed color

• Enhanced CSS variable handling

  • This was built upon feat: Add property for preserving css variables in token resolution #128, however instead of enabling through a feature flag, css variables will be the new default inheritance mechanism, for the reasons listed in that PR's description. Originally it was going to be a feature flag for runtime theming only, but it relies on also having the built theme (internal) enabling the flag as well.
  • Fixed transitive dependency tracking for context-overridden tokens
  • Improved transformer logic for nested var() references in non-global selectors
  • Better handling of mode vs context rule inheritance

• Reference token processing

  • Handles three input types: string seed, explicit palette, or hybrid (seed + overrides)
  • Mode-aware palette generation with proper merging of explicit overrides

• Code quality improvements

  • Extracted helper functions to reduce complexity in resolve.ts, transformer.ts, process.ts, and index.ts
  • Removed duplicate token collection logic
  • Added CSS variable reference extraction utilities

Testing

• Added palette generation spec and a11y tests
• Added runtime performance tests
• Dev pipeline

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[codecov]

Codecov Report

❌ Patch coverage is 99.60707% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.49%. Comparing base (e28b540) to head (d82bbb4).

Files with missing lines	Patch %	Lines
src/shared/theme/resolve.ts	98.09%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #130      +/-   ##
==========================================
+ Coverage   97.43%   97.49%   +0.05%     
==========================================
  Files          45       48       +3     
  Lines        2185     2591     +406     
  Branches      413      541     +128     
==========================================
+ Hits         2129     2526     +397     
- Misses         56       65       +9     

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