Feature/admin audit log UI

[uche102]

Summary

Exposes the platform audit logging system (#135) through a dedicated Admin UI and RBAC-restricted API endpoints. Authorized administrators can search, filter, inspect event details (including before/after state changes), export filtered results in CSV or JSON format, and trigger log retention purging.

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Acceptance Criteria Covered

• Searchable & Filterable Audit Log: Search across actors, actions, resources, resource IDs, and date ranges.
• Event Detail View: Modal displaying before/after state changes, request IP, user agent, and full metadata payload.
• Audit Result Exports: Export filtered audit records directly as CSV or JSON file downloads.
• Retention & Purging Controls: Configurable retention thresholds (30, 60, 90, 180, 365 days) with audit log purging.
• RBAC Restricted: Endpoints and UI access strictly enforced via authenticate and requireAdmin middleware.

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Key Implementation Details

1. Backend Service (backend/src/services/auditService.ts)

• Search & Filtering: Added $regex text matching across actor, action, resource, resourceId, and error messages.
• Exporting: Implemented exportLogs(options, format) producing formatted CSV or pretty-printed JSON output.
• Retention Purging: Added purgeOldLogs(retentionDays) to delete audit entries older than the retention threshold.

2. Admin Query Routes (backend/src/routes/admin/audit.ts)

• GET /api/admin/audit: Paginated, multi-field search and filter endpoints.
• GET /api/admin/audit/stats: Aggregated metrics for success/failure rates and top actors.
• GET /api/admin/audit/export: Triggers CSV or JSON download with Content-Disposition headers.
• POST /api/admin/audit/purge: Retention purging action ({ retentionDays: number }).
• GET /api/admin/audit/:id: Retrieves full details for a single audit event.
• Mounted under /api/admin/audit and /api/v1/admin/audit in backend/src/index.ts.

3. Frontend Admin UI (frontend/src/app/admin/audit/page.tsx)

• Metrics Summary Cards: Total entries, success operations, failure count, active actors.
• Interactive Data Table: Color-coded badges for actions and status, timestamp formatting, pagination controls.
• Event Detail Modal: Embedded syntax-highlighted viewer for inspecting before/after payload details.
• Export & Retention Modals: Direct CSV/JSON file generation and a purge confirmation dialog.
• Sidebar Integration: Added "Audit Logs" entry under Platform Operations in AdminSidebar.tsx.

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Files Changed

• backend/src/services/auditService.ts (Modified)
• backend/src/routes/admin/audit.ts (New)
• backend/src/index.ts (Modified)
• frontend/src/app/admin/audit/page.tsx (New)
• frontend/src/components/Admin/AdminSidebar.tsx (Modified)

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How to Test

1. Launch the backend and navigate to the admin audit endpoint or page:

   # Backend API
   GET /api/admin/audit?search=CREATE&result=success

-Closes #400