#63 API: List Tenants

Implement endpoint to list all tenants (system_admin only). Endpoint: GET /api/v1/tenants Query Parameters: - status: Filter by status (active, suspended, all) - page: Page number (default: 1) - per_page: Results per page (default: 50) Response: Paginated list of tenants with stats Required Permissions: system_admin only Implementation Requirements: - Include user count per tenant - Include workflow count per tenant - Include last activity timestamp - Include creation date - Include storage usage if applicable - Sort options: name, created, activity With ultra attention to details and correctness. Before closing: write comment summarizing implementation with screenshot.