[FE-54] Build Audit Log viewer — searchable, filterable timeline of all system changes

[yusuftomilola]

Overview

Admins need visibility into every change made across the system — who did what and when. The backend audit log endpoint (BE-67) provides this data. This issue builds the frontend viewer with search, filters, and a human-readable diff display.

Context

• Route: frontend/app/(dashboard)/audit-log/page.tsx (needs to be created)
• API endpoint: GET /audit-logs with query params: entityType, actorId, action, from, to, page, limit
• Visible to ADMIN users only — gate the page with a role check in middleware or the component
• Add "Audit Log" to the sidebar under Settings/Admin section

Acceptance Criteria

• Create frontend/app/(dashboard)/audit-log/page.tsx (ADMIN only)
• Timeline/table view with columns: Timestamp, Actor (name + avatar), Entity Type, Entity ID (linked to the relevant detail page), Action (coloured badge: green=CREATED, blue=UPDATED, red=DELETED), summary of change
• Filter bar: entity type dropdown, action dropdown, actor user selector, date range picker (from/to)
• Search input to filter by entity ID or actor name
• Clicking a row expands a diff view showing previous and new JSON values side-by-side (highlight changed fields)
• Pagination with "Load More" or numbered pages
• Create React Query hook: useAuditLogs(filters)