feat(select): add grouped select compound api

[singkia]

Adds Select.Group and Select.GroupLabel, docs example, tests, and regenerated registry metadata.

[pkg-pr-new]

npm i https://pkg.pr.new/@cloudflare/kumo@171

commit: 9368fb8

[github-actions]

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Commit: 9368fb8

[github-actions]

Visual Regression Report

23 screenshot(s) with visual changes:

Button / Variants

0 px (0%) changed

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Button / Sizes

0 px (0%) changed

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Button / With Icon

0 px (0%) changed

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Button / Icon Only

0 px (0%) changed

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Button / Loading State

4 px (0%) changed

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Button / Disabled State

0 px (0%) changed

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Dialog / Basic Dialog

86,865 px (1.66%) changed

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Dialog / Alert Dialog (role="alertdialog")

125,752 px (2.4%) changed

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Dialog / Confirmation Dialog (with disablePointerDismissal)

133,606 px (2.55%) changed

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Dialog / With Actions

0 px (0%) changed

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Dialog / With Select

129,554 px (2.47%) changed

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Dialog / With Combobox

129,597 px (2.47%) changed

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Dialog / With Dropdown

124,316 px (2.37%) changed

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Dialog (Open)

149 px (0%) changed

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Select / Basic Usage

18,246 px (3.28%) changed

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Select / Placeholder

37,033 px (5.66%) changed

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Select / Custom Rendering

920 px (0.06%) changed

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Select / Loading

38,573 px (5.93%) changed

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Select / Multiple Item

807,100 px (49.11%) changed

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Select / More Example

42,926 px (4.8%) changed

Before	After	Diff

Select / Select

5,361 px (0.62%) changed

Before	After	Diff

Select / Select.Option

5,361 px (0.62%) changed

Before	After	Diff

Select (Open)

3,340,172 px (21.22%) changed

Before	After	Diff

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Generated by Kumo Visual Regression

[singkia]

Rebased this PR onto the latest main and resolved the merge conflicts. The branch is now mergeable again.

It looks like the new workflow runs for this fork-based PR are currently in action_required state and have not started any jobs yet, so they may be waiting for maintainer approval before CI can proceed.