[Hardening] F-03: Recommended Mandatory 2FA Enforcement from the Start.

### The required feature described as a wish

**Description:** The "Tyranny of Default" principle recommends enabling the global setting `mandate.user.2fa` from the start. Security can always be downgraded later, but most users will simply accept whatever defaults they are given. If `mandate.user.2fa` is not set, 2FA remains ineffective even for those users who have already enrolled.

**Affected Components:** Management UI

**Impact:** Without mandatory enforcement, users may choose not to enroll in 2FA. In environments with regulatory or compliance requirements (e.g., PCI-DSS, SOC 2), the absence of enforced MFA may constitute a compliance gap.

**Steps to Reproduce:**
- Log in to the CloudStack Management UI as a Root Admin.
- Navigate to Configuration > Global Settings.
- Search for `mandate.user.2fa` and confirm the value is False.
- Create a new user account at any permission level.
- Log in as that user and confirm that access is granted without any 2FA prompt.

**Recommended Remediation:** Set `mandate.user.2fa` to True by default. Users will be naturally guided to set up 2FA at first login without friction, and the first impression of the ACS project will reflect a stronger security posture.

從 CloudStack Management UI 的 Global Settings 開始，找到 `mandate.user.2fa` 的定義。檢查其預設值如何套用，以及如何驗證首次登入時的強制要求；當新安裝預設啟用此設定，並提示新建立的使用者設定 2FA 時，即表示完成。

由索引模型根據 Issue 內容生成。