[Hardening] F-02: Default Configuration Forces User’s Posture to Password-Only.

### The required feature described as a wish

**Description:** the global configuration setting `enable.user.2fa` defaults to False, meaning users who wish to use two-factor authentication (2FA) cannot do so without a Root Admin first enabling the setting and restarting the management server(s).

**Affected Components:** Management UI

**Impact:** Any compromised or weak user credential is sufficient to gain full access to a user's CloudStack account. This makes the platform susceptible to credential-stuffing, phishing, and brute-force attacks with no second factor to impede unauthorized access.

**Steps to Reproduce:**
- Log in to the CloudStack Management UI as a Root Admin.
- Navigate to Configuration > Global Settings.
- Search for `enable.user.2fa` and observe that its value is set to False.
- Attempt to enable 2FA on your own user account, and confirm that it is not permitted.

**Recommended Remediation:** Change the default value of `enable.user.2fa` to True so that users are always permitted to enroll in 2FA without requiring Root Admin intervention.

從 Management UI 中 Global Settings 對 enable.user.2fa 的處理著手，並確認其預設值如何控制使用者註冊。預設值允許使用者在不需 Root Admin 介入或重新啟動 management-server 的情況下註冊 2FA 後，即表示變更完成；在 UI 中確認該設定與註冊流程。

由索引模型根據 Issue 內容生成。