fix: show a translated notice when the sign-in session expired

The sign-in screen showed the auth store's raw English error ("Session
expired", "Invalid username or password") as the notice title. It now
runs it through describeLoginError like every other sign-in failure,
which also learns to explain an expired session with the webmail's
login.session_expired copy. The back and close buttons of the sign-in
steps get screen reader labels, and the email placeholders use the
webmail's translated example address.

src/components/__tests__/screens-i18n.test.ts

@@ -17,6 +17,17 @@ const TRANSLATED_FILES: Record<string, string[]> = {
   // The link prompt shows an example URL.
   'screens/ComposeScreen.tsx': ['https://example.com'],
   'components/RichTextEditor.tsx': [],
+  'screens/LoginScreen.tsx': [],
+  // Product name and example host.
+  'screens/login/ChooseStep.tsx': ['Bulwark Mail'],
+  'screens/login/ConfirmStep.tsx': [],
+  'screens/login/EmailStep.tsx': [],
+  'screens/login/LoginNotice.tsx': [],
+  'screens/login/LoginShell.tsx': ['Bulwark Mobile v'],
+  'screens/login/OptionTile.tsx': [],
+  'screens/login/PasswordStep.tsx': [],
+  'screens/login/ServerStep.tsx': ['mail.example.com'],
+  'screens/login/SigningInStep.tsx': [],
   'screens/ScheduledScreen.tsx': [],
   'screens/EmailSourceScreen.tsx': [],
   'components/OfflineBanner.tsx': [],