feat: implement check and uncheck habit functionality

Allow users to mark habits as completed and uncompleted for the current day.

Goal:
Enable daily tracking by letting users toggle habit completion status.

Features:
- Tap on a habit to mark it as completed
- Tap again to uncheck it
- Update today's daily document in Firestore
- Reflect UI changes instantly (checked state, visual feedback)
- Recalculate daily progress after toggle