feat: add React faceted search sample

[vystartasv]

Description

Adds a React faceted search web part using the read-only SharePoint Search REST API. Users can search the current site, inspect bounded results, and filter them with returned FileType and ContentClass refiners.

What changed

• Added SharePoint Search REST query construction with encoded parameters.
• Added bounded query, paging, refiner, and control-character validation.
• Added safe HTTP result-link handling.
• Added accessible Fluent UI search, filters, result cards, loading, empty, error, and retry states.
• Added dependency-free response mapping and error-classification tests.
• Added README and valid gallery metadata.

How was this tested?

• npm ci
• npm test -- --clean — 4/4 tests passed.
• npm run build — TypeScript, Sass, webpack, and lint phase passed.
• npm run package-solution — production .sppkg package generated and validated.
• Removed generated dependencies and build artifacts before commit.

Tenant validation requested

Please validate the SharePoint Search REST behavior in a SharePoint Online tenant and add a real screenshot if possible. Search indexing, result properties, refiners, permissions, and responsive behavior need tenant confirmation.

Type of change

• New sample
• Tests included
• Documentation included
• No fabricated tenant screenshots

[vystartasv]

Could someone with SharePoint Online access please validate this sample in a real tenant and add a representative screenshot to assets/ or this PR if possible?

Please check search indexing/results, FileType and ContentClass refiners, permissions, empty/error/retry states, and narrow web-part widths. The implementation is read-only and uses SharePoint Search REST only. Local tests, TypeScript, webpack, lint, and production packaging pass. Thank you for any positive or negative findings!

[github-actions]

Validation failed!

File: samples/react-faceted-search/assets/sample.json

• Missing 'name' property!
• Missing 'source' property!
• Missing 'title' property!
• Missing 'shortDescription' property!
• Missing 'url' property!
• Missing 'creationDateTime' property!
• Missing 'updateDateTime' property!
• Missing 'products' property!
• Missing 'thumbnails' property!

[github-actions]

Sample PR validation for #6480

⚠️ 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 #6480

⚠️ 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 #6480

⚠️ 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.