#40 [Admin Panel] User Management API - Update User

Implement PUT /api/v1/admin/users/<user_id> endpoint to update user information. **API Specification:** - Endpoint: PUT /api/v1/admin/users/<user_id> - Permission Required: manage_users - Path Parameter: user_id (UUID) - Request Body: {display_name?, email?, is_active?, metadata?} - Response: Updated user object **Requirements:** - Partial updates supported (only provided fields updated) - Email change requires re-verification - Cannot change own is_active status (prevent self-lockout) - Log audit event for all changes with before/after values - Validate email uniqueness if changing email - Return 404 if user not found, 409 if email conflict **Audit Log Entry:** - action: user_updated - user_id, changed_by, changed_fields[], old_values{}, new_values{} **IMPORTANT:** Implement with ultra attention to details and correctness. **BEFORE CLOSING:** Take screenshot showing user update. Add comment summarizing implementation.