feat: add React accessibility content auditor sample

[vystartasv]

Description

Adds a read-only React accessibility and content quality auditor for SharePoint Framework 1.23.2.

What changed

• Audits bounded, allow-listed SharePoint content fields.
• Reports missing alt text, empty/non-descriptive links, skipped heading levels, and empty required content.
• Provides severity, rule, evidence, item, and safe remediation URL.
• Includes loading, empty, partial-failure, access-denied, retry, keyboard, and responsive states.
• Documents heuristic scope, permissions, limits, and tenant validation.

Validation

• npm test — 15 tests passed.
• npm run build — DEBUG/SHIP build and production .sppkg packaging passed.
• Generated outputs removed before commit.
• Diff checked for scope, secrets, and unrelated files.

This is a heuristic review aid, not a WCAG conformance certification, and performs no content mutations.

[vystartasv]

Could someone with a SharePoint Online tenant please validate this sample against representative modern pages or list content and add real screenshots to the PR if possible?

Useful checks:

• Missing alt-text findings on images.
• Empty and generic link-text findings.
• Heading-order detection.
• Required-field and malformed-content handling.
• Permission-denied, throttling, retry, keyboard, and responsive states.
• Whether remediation links remain correct on a managed-path site.

This is intentionally a read-only heuristic audit aid, not a WCAG certification tool. No tenant screenshots are fabricated locally. Thank you for helping complete the review.

[github-actions]

Validation failed!

File: samples/react-accessibility-content-auditor/assets/sample.json

• Missing 'thumbnails' property!

[github-actions]

Sample PR validation for #6483

⚠️ Validation status: warnings

We automatically validate all pull requests against our contribution guidance to ensure that all samples provide a consistent experience to our community.

In order to merge this PR in a timely manner, the following criteria must be met:

Validation	Status
Pull request affects only one folder	✅ Succeeded
Sample folder name follows naming convention	✅ Succeeded
README.md contains visitor stat image	⚠️ Warning
Sample requires a .nvmrc file	✅ Succeeded
Sample requires a README.md	✅ Succeeded
Sample requires a screenshot .png in assets folder	⚠️ Warning
No .sppkg file	✅ Succeeded
No node_modules folder	✅ Succeeded
No lib folder	✅ Succeeded
No upgrade reports	✅ Succeeded

@vystartasv please address the above issues and push new changes to this branch.
For more information, see the contribution guidance.

[github-actions]

Sample PR validation for #6483

⚠️ Validation status: warnings

We automatically validate all pull requests against our contribution guidance to ensure that all samples provide a consistent experience to our community.

In order to merge this PR in a timely manner, the following criteria must be met:

Validation	Status
Pull request affects only one folder	✅ Succeeded
Sample folder name follows naming convention	✅ Succeeded
README.md contains visitor stat image	⚠️ Warning
Sample requires a .nvmrc file	✅ Succeeded
Sample requires a README.md	✅ Succeeded
Sample requires a screenshot .png in assets folder	⚠️ Warning
No .sppkg file	✅ Succeeded
No node_modules folder	✅ Succeeded
No lib folder	✅ Succeeded
No upgrade reports	✅ Succeeded

@vystartasv please address the above issues and push new changes to this branch.
For more information, see the contribution guidance.

[github-actions]

Sample PR validation for #6483

⚠️ Validation status: warnings

We automatically validate all pull requests against our contribution guidance to ensure that all samples provide a consistent experience to our community.

In order to merge this PR in a timely manner, the following criteria must be met:

Validation	Status
Pull request affects only one folder	✅ Succeeded
Sample folder name follows naming convention	✅ Succeeded
README.md contains visitor stat image	✅ Succeeded
Sample requires a .nvmrc file	✅ Succeeded
Sample requires a README.md	✅ Succeeded
Sample requires a screenshot .png in assets folder	⚠️ Warning
No .sppkg file	✅ Succeeded
No node_modules folder	✅ Succeeded
No lib folder	✅ Succeeded
No upgrade reports	✅ Succeeded

@vystartasv please address the above issues and push new changes to this branch.
For more information, see the contribution guidance.