fix(auth): do not show MFA button when the project does not have MFA enabled

[megastep]

This is a simple change to the SignedIn view to conditionally disable showing the manage MFA button when this feature is not enabled in the Firebase project, to prevent user confusion.

Also added a corresponding UI test for this behavior.

[gemini-code-assist]

Code Review

This pull request introduces conditional visibility for the MFA management button in SignedInView based on the authentication configuration. Feedback includes a suggestion to mark the internal helper property as private for better encapsulation and a recommendation to add UI or view-level tests to verify the button's presence in the hierarchy, as the current unit tests only validate the underlying logic.

[russellwheatley]

@megastep - thank you, this does indeed look like a UI issue that we ought to address. I'll take a look at this a bit more in-depth and provide some feedback 🙏

[russellwheatley]

Hey @megastep - do you mind merging with main? I tried but it seems that you have protected it. It should resolve CI failures 🙏

[megastep]

@russellwheatley ok, done!