Add push notification functionality with tests and digest scheduler

- Implemented push subscription API with tests for subscribing and unsubscribing users.
- Created web push notification tests triggered by child actions.
- Added digest scheduler to send email digests to users at 9 PM local time.
- Developed utility functions for creating and validating digest action tokens.
- Integrated web push sender to handle sending notifications to users.
- Added service worker for handling push notifications in the frontend.
- Created a push opt-in component for user notification preferences.
- Implemented tests for the push opt-in component to ensure correct behavior.
- Updated frontend services to manage push subscriptions and permissions.

backend/models/user.py

@@ -22,6 +22,8 @@ class User(BaseModel):
     deletion_attempted_at: str | None = None
     role: str = 'user'
     token_version: int = 0
+    timezone: str | None = None
+    email_digest_enabled: bool = True
 
     @classmethod
     def from_dict(cls, d: dict):
@@ -45,6 +47,8 @@ class User(BaseModel):
             deletion_attempted_at=d.get('deletion_attempted_at'),
             role=d.get('role', 'user'),
             token_version=d.get('token_version', 0),
+            timezone=d.get('timezone'),
+            email_digest_enabled=d.get('email_digest_enabled', True),
             id=d.get('id'),
             created_at=d.get('created_at'),
             updated_at=d.get('updated_at')
@@ -73,5 +77,7 @@ class User(BaseModel):
             'deletion_attempted_at': self.deletion_attempted_at,
             'role': self.role,
             'token_version': self.token_version,
+            'timezone': self.timezone,
+            'email_digest_enabled': self.email_digest_enabled,
         })
         return base