chore(progress-circle): add vrt support

[cdransf]

Description

Adds Storybook VRT coverage for progress-circle: independent size and state rows (indeterminate, 0/25/50/75/100 determinate, one labeled row per state so indeterminate can't collide visually with a determinate value), static-color states on contrast backgrounds, forced-colors, and custom-property reference/override rows; test-only, no runtime code changes.

Motivation and context

SWC-2412 requires VRT coverage for progress-circle following the button/divider/card/meter VRT foundation (#6463); no global-styles VRT file since the component has no plain-element equivalent, and no reduced-motion story since no existing tooling in this repo can force that media feature.

Related issue(s)

• fixes SWC-2412

Author's checklist

• I have read the CONTRIBUTING and PULL_REQUESTS documents.
• I have reviewed the Accessibility Practices for this feature, see: Aria Practices
• I have added automated tests to cover my changes.
• I have included a well-written changeset if my change needs to be published.
• I have included updated documentation if my change required it.

Accessibility testing checklist

• Keyboard: no focusable parts added; progress-circle is non-interactive, so no keyboard flow to verify beyond confirming no regressions in existing stories.
• Screen reader: new stories only exercise existing behavior (role="progressbar", aria-valuenow/aria-valuetext on determinate, label fallback on indeterminate); confirm announcements are unchanged from pre-existing coverage.

[changeset-bot]

⚠️ No Changeset found

Latest commit: d2fa025

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[github-actions]

📚 Branch Preview Links

• Storybook (Gen2, dev mode)
• Storybook (Gen2, prod mode)
• Documentation Site (Gen1)
• Storybook (Gen1)

🔍 Gen1 Visual Regression Test Results

When a visual regression test fails (or has previously failed while working on this branch), its results can be found in the following URLs:

• Spectrum | Light | Medium | LTR
• Spectrum | Dark | Large | RTL
• Express | Light | Medium | LTR
• Express | Dark | Large | RTL
• Spectrum-two | Light | Medium | LTR
• Spectrum-two | Dark | Large | RTL
• High Contrast Mode | Medium | LTR

Deployed to Azure Blob Storage: pr-6600

If the changes are expected, update the current_golden_images_cache hash in the circleci config to accept the new images. Instructions are included in that file.
If the changes are unexpected, you can investigate the cause of the differences and update the code accordingly.