Configure "delete account" button behavior

[megastep]

This makes the "Delete Account" button in the SignedInView configurable, for cases when the application needs more advanced account deletion configuration:

• Existing behavior (default) with confirmation dialog;
• Button disabled; or
• Custom action on clicking

This also includes the changes from my previous PR #1338 to disable the MFA button if that is turned off in the project's configuration.

Also fixes some missing localized strings in the dialog, even though the strings were already localized.

[gemini-code-assist]

Code Review

This pull request introduces the ability to customize the account deletion button behavior in SignedInView via the AuthConfiguration. It adds a new DeleteAccountButtonAction enum allowing the button to be shown with a default confirmation sheet, hidden entirely, or linked to a custom action. Additionally, it includes UI updates to conditionally display the MFA management and delete account buttons, localizes strings in the deletion confirmation sheet, and adds corresponding unit tests and documentation. I have no feedback to provide.