Firebase gives you cross-device sync, streaks that persist, and optional push reminders. Takes ~15 minutes. The app works without it using local storage.
1
Create Firebase Project
Go to firebase.google.com → Add project → Enter any name → Continue through prompts.
2
Enable Google Sign-in
In Firebase console → Authentication → Sign-in method → Enable Google. Set your email as authorized.
3
Create Firestore Database
Firestore Database → Create database → Start in production mode → Choose nearest region.
4
Get Web Config
Project settings (gear icon) → Your apps → Add web app → Copy the firebaseConfig object.