Schema design

class User(UserMixin, Model):
    email = db.Column(db.String(255), unique=True)  # OAuth identity
    stripe_customer_id = db.Column(db.String(255))  # for the billing portal
    # NO subscription_status, NO quota, NO content here

class Account(Model):
    name = db.Column(db.String(100))               # "Family", "Work", etc.
    owner_user_id = db.Column(db.ForeignKey("users.id"))
    quota = db.Column(db.Integer, default=0)       # usage limits here

class AccountUser(Model):
    user_id = db.Column(db.ForeignKey("users.id"), primary_key=True)
    account_id = db.Column(db.ForeignKey("accounts.id"), primary_key=True)
    role = db.Column(db.String(20))  # "admin", "member", "child"

class Subscription(Model):
    account_id = db.Column(db.ForeignKey("accounts.id"))
    stripe_subscription_id = db.Column(db.String(255))
    status = db.Column(db.String(50))     # "active", "canceled", etc.
    tier_name = db.Column(db.String(50))  # "Basic", "Pro", "Enterprise"