feat(biometric-trust): show explanatory subtitle on enrollment-change unlock

When handleLocalAuthentication invalidates biometric trust because the device
enrolment set changed, the passcode modal now displays an explanatory
subtitle reading "Biometric enrollment changed, please use your passcode".

The signal travels over LOCAL_AUTHENTICATE_EMITTER's existing reason payload
(added in the previous commit). PasscodeEnter reads reason from props,
mirrors it into local state so a button-triggered invalidation can update it
without re-emitting, and renders Base's subtitle slot only when
reason === 'enrollmentChanged'. The subtitle clears naturally on the next
modal open because reason is reinitialised from props each session.

Normal auto-lock unlocks, cancel/error fallbacks, and re-opens after a
successful unlock leave the subtitle hidden — it is strictly tied to the
invalidation event.

Part of VLN-216.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: OtavioStasiak

app/containers/Passcode/PasscodeEnter.test.tsx

@@ -92,3 +92,23 @@ describe('PasscodeEnter biometry button', () => {
 		expect(getByTestId('biometry-button')).toBeTruthy();
 	});
 });
+
+describe('PasscodeEnter enrollmentChanged subtitle', () => {
+	beforeEach(() => {
+		jest.clearAllMocks();
+	});
+
+	it('renders explanatory subtitle when reason === "enrollmentChanged"', () => {
+		const { getByText } = render(
+			<PasscodeEnter hasBiometry={false} skipAutoBiometry reason='enrollmentChanged' finishProcess={jest.fn()} />
+		);
+
+		expect(getByText('Local_authentication_biometric_enrollment_changed')).toBeTruthy();
+	});
+
+	it('does not render subtitle when reason is undefined', () => {
+		const { queryByText } = render(<PasscodeEnter hasBiometry={false} skipAutoBiometry finishProcess={jest.fn()} />);
+
+		expect(queryByText('Local_authentication_biometric_enrollment_changed')).toBeNull();
+	});
+});

app/containers/Passcode/PasscodeEnter.tsx

@@ -36,9 +36,7 @@ const PasscodeEnter = ({
 	// biometry button immediately hides the button within the same modal session, without
 	// re-emitting LOCAL_AUTHENTICATE_EMITTER (which would orphan the upstream openModal promise).
 	const [hasBiometry, setHasBiometry] = useState<boolean>(initialHasBiometry);
-	// `reason` is held for slice 03's subtitle copy; _reason intentionally unused for now.
-	// eslint-disable-next-line @typescript-eslint/no-unused-vars
-	const [_reason, setReason] = useState<BiometricInvalidationReason | undefined>(initialReason);
+	const [reason, setReason] = useState<BiometricInvalidationReason | undefined>(initialReason);
 	const { setItem: setAttempts } = useAsyncStorage(ATTEMPTS_KEY);
 	const { setItem: setLockedUntil } = useAsyncStorage(LOCKED_OUT_TIMER_KEY);
 
@@ -103,11 +101,14 @@ const PasscodeEnter = ({
 		return <Locked setStatus={setStatus} />;
 	}
 
+	const subtitle = reason === 'enrollmentChanged' ? I18n.t('Local_authentication_biometric_enrollment_changed') : null;
+
 	return (
 		<Base
 			ref={ref}
 			type={TYPE.ENTER}
 			title={I18n.t('Passcode_enter_title')}
+			subtitle={subtitle}
 			showBiometry={hasBiometry}
 			onEndProcess={onEndProcess}
 			onBiometryPress={biometry}