WEBDEV-8503 Migrate ia-button to elements

[rebecca-shoptaw]

Moves the ia-button component from Offshoot into Elements. It's mostly a simple copy-paste, with the only big difference being switching from using parent-applied classes for styling, to using a property called mode, i.e. <ia-button class="primary"> -> <ia-button mode="primary">

Also renames the CSS variables to match our new conventions and creates a set of theme variables where needed.

[github-actions]

PR Preview Action v1.8.1
Preview removed because the pull request was closed.
2026-06-02 19:05 UTC

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.45%. Comparing base (6661c83) to head (1cddcd1).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/elements/ia-button/ia-button.ts	50.00%	12 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #56      +/-   ##
==========================================
- Coverage   79.66%   78.45%   -1.21%     
==========================================
  Files          16       16              
  Lines         659      687      +28     
  Branches      177      186       +9     
==========================================
+ Hits          525      539      +14     
- Misses         90      102      +12     
- Partials       44       46       +2     

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[latonv]

LGTM, nice migration! Spotted one possible typo.