Initial commit: habit tracker PWA with Google OAuth, push notifications

FastAPI + SQLAlchemy/Alembic + MariaDB backend with Jinja2/htmx/Alpine
server-rendered frontend. Multi-user via Google OAuth, daily habit
tracking, monthly/weekly history views, Web Push reminders via
APScheduler, and PWA support (manifest, service worker, offline caching).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/models/push_subscription.py

@@ -0,0 +1,21 @@
+from datetime import datetime
+
+from sqlalchemy import ForeignKey, Integer, String
+from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+
+class PushSubscription(Base):
+    __tablename__ = "push_subscription"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+    user_id: Mapped[int | None] = mapped_column(
+        ForeignKey("user.id", ondelete="CASCADE"), nullable=True
+    )
+    endpoint: Mapped[str] = mapped_column(String(512), nullable=False, unique=True)
+    p256dh_key: Mapped[str] = mapped_column(String(255), nullable=False)
+    auth_key: Mapped[str] = mapped_column(String(255), nullable=False)
+    user_agent: Mapped[str | None] = mapped_column(String(255), nullable=True)
+    created_at: Mapped[datetime] = mapped_column(server_default=func.now(), nullable=False)