feat(admin): implement hub settings page and React Query integration

[mijinummi]

🧪 QA: Admin Hub Settings Page UI Testing Guide (#1300)

Closes #1300

Description

This PR introduces the official UI Manual Testing Guide for the Admin Hub Settings page (/admin/settings), covering Issue #1300. It outlines a structured, step-by-step test plan designed to verify operational controls across all 5 tabbed sections (General, Booking Rules, Business Hours, Financial, and Branding).

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Test Coverage Summary

• Access & Navigation: Authorization checks and default state loading on /admin/settings.
• General Tab: Input verification and payload accuracy for basic hub contact details.
• Booking Rules Tab: Numeric bound validations for lead time, max days ahead, and cancellation windows.
• Business Hours Tab:
  • Verification of 30-minute interval constraints across open/close time pickers.
  • Verification of day-level "Closed" toggles disabling input pickers.
• Financial Tab: Read-only validation for currency (NGN) and percentage inputs for VAT.
• Branding Tab: Synchronization between hex text inputs and color picker UI controls.
• Error & Edge Cases: Graceful fallback handling on network failures (500 status) and invalid field submissions.

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Verification Strategy

Reviewers and QA engineers should use the steps outlined in the test guide document to manually validate:

1. Isolated section payload delivery (PATCH /hub-settings containing only active tab keys).
2. Toast feedback behavior on HTTP 200 success vs. 4xx/5xx error responses.
3. State persistence upon browser refresh.

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Related Resources & Dependencies

• Issue: [FE-42] Admin hub settings page (/admin/settings) #1300
• Backend Dependency: BE-54 (GET /hub-settings & PATCH /hub-settings)
• Branding Linkage: FE-38 (White-labeling support)

[vercel]

@mijinummi is attempting to deploy a commit to the naijabuz's projects Team on Vercel.

A member of the Team first needs to authorize it.

[yusuftomilola]

@mijinummi Kindly fix CI not passing

[mijinummi]

Alright sir, on it