feat: add React resource capacity planner

[vystartasv]

Description

Adds a read-only React room and shared-resource capacity planner for SPFx 1.23.2.

What changed

• Loads bounded SharePoint REST resources and reservations with GET only.
• Calculates daily/weekly utilization against configured working-hour capacity.
• Detects deterministic half-open interval overlaps and exposes available slots.
• Validates HTTPS same-tenant REST URLs, field names, resource IDs, ISO dates, time zones, horizons, page sizes, and item limits.
• Handles empty, malformed, partial, permission, throttling, retry, and generic error states.
• Provides responsive, keyboard-accessible, non-color-only table/card views.
• Does not create, update, or cancel bookings and requests no additional API permissions.

Validation

• npm ci
• npm test — 8 tests passed.
• npm run verify — GET-only verifier passed.
• npm run build — SPFx bundle passed.
• gulp package-solution --ship — production package passed.
• Gallery metadata, configuration, scope, diff, and secret scans passed.
• Generated artifacts removed before commit.

Tenant validation requested

Please validate representative SharePoint room/resource and reservation lists, including overlapping and touching intervals, multi-unit resources, empty data, malformed records, partial failures, limited permissions, throttling, managed paths, date horizons, time-zone display, keyboard access, and responsive layout. Real tenant screenshots are welcome; none are fabricated locally.

The sample intentionally uses SharePoint REST rather than silently assuming Microsoft Graph Bookings or Exchange permissions. It is a read-only planning view, not a booking system.

[vystartasv]

Could someone with a SharePoint Online tenant please validate PR #6487 and add real screenshots if possible?

Please test representative room/resource and reservation lists, including:

• Daily/weekly utilization and capacity calculations.
• Overlapping intervals, touching intervals, and multi-unit resources.
• Available slots and conflict indicators.
• Empty, malformed, partial, permission-denied, throttled, retryable, and generic failures.
• Managed-path URLs, date horizons, time-zone display, keyboard navigation, and responsive layout.

The sample is SharePoint REST GET-only. It does not create, update, or cancel bookings and requests no additional API permissions. It is a planning view, not a booking system. Real tenant screenshots only; none are fabricated locally.

[github-actions]

Sample PR validation for #6487

⚠️ 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 #6487

⚠️ 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.