#62 API: Create Tenant

Implement endpoint to create a new tenant (system_admin only). Endpoint: POST /api/v1/tenants Request Body: - name: string (required, unique) - display_name: string (optional) - settings: object (optional, tenant-specific settings) - admin_email: string (required, first admin user) Response: Created tenant with encrypted client key Required Permissions: system_admin only Implementation Requirements: - Generate unique tenant ID (UUID) - Generate encrypted client key (Fernet) - Create default roles for tenant - Send invitation to admin email - Initialize tenant settings - Create tenant-specific database schemas if needed With ultra attention to details and correctness. Before closing: write comment summarizing implementation with screenshot.