Add e-mail-based sign in challenge for users with disabled 2FA (#14013)

config/locales/en.yml

@@ -1273,6 +1273,12 @@ en:
       explanation: You requested a full backup of your Mastodon account. It's now ready for download!
       subject: Your archive is ready for download
       title: Archive takeout
+    sign_in_token:
+      details: 'Here are details of the attempt:'
+      explanation: 'We detected an attempt to sign in to your account from an unrecognized IP address. If this is you, please enter the security code below on the sign in challenge page:'
+      further_actions: 'If this wasn''t you, please change your password and enable two-factor authentication on your account. You can do so here:'
+      subject: Please confirm attempted sign in
+      title: Sign in attempt
     warning:
       explanation:
         disable: While your account is frozen, your account data remains intact, but you cannot perform any actions until it is unlocked.
@@ -1310,11 +1316,14 @@ en:
       title: Welcome aboard, %{name}!
   users:
     follow_limit_reached: You cannot follow more than %{limit} people
+    generic_access_help_html: Trouble accessing your account? You may get in touch with %{email} for assistance
     invalid_email: The e-mail address is invalid
     invalid_otp_token: Invalid two-factor code
+    invalid_sign_in_token: Invalid security code
     otp_lost_help_html: If you lost access to both, you may get in touch with %{email}
     seamless_external_login: You are logged in via an external service, so password and e-mail settings are not available.
     signed_in_as: 'Signed in as:'
+    suspicious_sign_in_confirmation: You appear to not have logged in from this device before, and you haven't logged in for a while, so we're sending a security code to your e-mail address to confirm that it's you.
   verification:
     explanation_html: 'You can <strong>verify yourself as the owner of the links in your profile metadata</strong>. For that, the linked website must contain a link back to your Mastodon profile. The link back <strong>must</strong> have a <code>rel="me"</code> attribute. The text content of the link does not matter. Here is an example:'
     verification: Verification

config/locales/simple_form.en.yml

@@ -151,6 +151,7 @@ en:
         setting_use_blurhash: Show colorful gradients for hidden media
         setting_use_pending_items: Slow mode
         severity: Severity
+        sign_in_token_attempt: Security code
         type: Import type
         username: Username
         username_or_email: Username or Email