feat: Admin audit log UI, events management, and announcements broadcast pages

[JoeX17]

Summary

This PR implements four features assigned to JoeX17:

[FE-26] Admin Audit Log: Frontend (#1206)

• /admin/audit-log page with data table: Actor, Action, Resource Type, Resource ID, Date/Time, IP Address
• Filters: resource type dropdown, date-range start/end date pickers
• Expandable rows — clicking a row expands to show the full metadata JSON in a formatted code block
• Read-only page (no action buttons — audit records are immutable)
• Page shows an "access restricted" message for non-super_admin users
• useGetAuditLog React Query hook with filtering and pagination support

[FE-27] Admin Events Management Page: Frontend (#1207)

• /admin/events page with events table: Title, Start Date, Capacity, Status badge (Upcoming/Cancelled), Actions
• Create Event button → form modal with: title, host name, start/end datetime, capacity, description fields
• Row action: Cancel button (with confirmation) calls DELETE /events/:id
• useGetAdminEvents, useCreateEvent, useUpdateEvent, useCancelEvent React Query hooks

[BE-30] Admin Announcements / Broadcast Messaging: Backend (#1208)

• Broadcast announcements leverage the existing AnnouncementsModule (POST /announcements, GET /announcements, GET /announcements/:id)
• The existing implementation handles admin-created announcements with author attribution and optional expiry
• Frontend integration via useSendAnnouncement hook

[FE-28] Admin Announcements: Frontend (#1209)

• /admin/announcements page listing past announcements with title, body excerpt, and sent date
• New Announcement button → modal composer with: Title, Audience dropdown (ALL_MEMBERS/ACTIVE_MEMBERS/STAFF), Channel dropdown (IN_APP/EMAIL/BOTH), body textarea
• Sent announcements are read-only in the list
• useGetAnnouncements and useSendAnnouncement React Query hooks

Closes #1206
Closes #1207
Closes #1208
Closes #1209

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