[FE-42] Admin hub settings page (/admin/settings)

[yusuftomilola]

Overview

Hub operators have no UI to configure operational settings — business hours, booking rules, tax rates, and branding are all hardcoded or environment-variable-only. The hub settings page gives operators full control without touching config files.

Context

• Admin pages pattern: frontend/app/admin/members/page.tsx
• Depends on BE-54 for GET /hub-settings and PATCH /hub-settings
• Branding settings link with white-labeling (FE-38)

Tasks

• Create /admin/settings page with tabbed sections:
  • General: Hub name, address, city, country, contact email, contact phone — editable fields with a "Save" button
  • Booking Rules: Lead time (hours), max days ahead, cancellation policy hours — numeric inputs
  • Business Hours: Day-of-week toggle + open/close time pickers for Mon–Sun; "Closed" toggle per day
  • Financial: VAT rate percent input (e.g. 7.5), currency display (read-only, NGN)
  • Branding: Logo upload (Cloudinary), primary colour hex picker, favicon upload
• Each tab section has its own "Save Changes" button that calls PATCH /hub-settings with only that section's fields
• Show a success toast on save and an error toast if the request fails
• Business hours picker: time inputs constrained to 30-minute intervals; "Closed" toggle disables the time inputs for that day
• Create useGetHubSettings and useUpdateHubSettings React Query hooks

Files to Modify / Create

• New: frontend/app/admin/settings/page.tsx
• New: frontend/lib/react-query/hooks/admin/settings/useGetHubSettings.ts
• New: frontend/lib/react-query/hooks/admin/settings/useUpdateHubSettings.ts