Add option to disable email verification check in authentication settings

Description The email verification check added in #12605 (v1.8.1) breaks sign-in for Azure AD accounts that lack the mail attribute — common with external/contractor accounts in enterprise tenants. Problem We use Azure AD SSO with contractor accounts. These accounts don't have the mail attribute set in Azure AD, so Microsoft returns xms_edov = false. Combined with our allowed domains configuration, this causes the new check in userProvisioner to reject sign-in. The Azure AD admin cannot modify the mail attribute for these external accounts. Other accounts with the mail attribute set work fine — only those without it are affected. Proposal Add a toggle in Settings → Authentication to allow workspace admins to disable the email verification requirement: • "Require verified email for sign-in" — enabled by default (preserving current security behavior), can be disabled per workspace. This would be consistent with how allowed domains is alread…