Implements MS21-API-001, MS21-API-002, MS21-API-005: Admin API endpoints
for user management (list, invite, update, deactivate) and workspace
management (create, update). All routes protected by AuthGuard + AdminGuard.
Endpoints:
- GET /api/admin/users (paginated)
- POST /api/admin/users/invite
- PATCH /api/admin/users/:id
- DELETE /api/admin/users/:id (soft-delete via deactivatedAt)
- POST /api/admin/workspaces
- PATCH /api/admin/workspaces/:id
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>