Test Android Chronometer

Send the Android streak-saver chronometer push to one user's device for testing.

Android counterpart of /admin/test-live-activity: fires the exact Expo data push the streak-loss cron sends (type="streak" + the user's local-midnight deadline); the app's native FCM handler renders the ongoing countdown notification. Deliberately BYPASSES the android_streak_chronometer_enabled feature flag so the flow stays testable in production while the cron is dormant — single-user only, so there is no broadcast risk.

• x-user-id (header): user to send to (must have stored Expo push_tokens)
• Body (optional): {"streakCount": N} to override the count shown; defaults to 7.
• Requires x-api-key header for authentication.