WIP checkpoint: Scaffold FastAPI backend project structure

backend/app/models/session.py

@@ -0,0 +1,18 @@
+from sqlalchemy import Column, String, DateTime, ForeignKey, Boolean
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+from app.database import Base
+
+
+class Session(Base):
+    __tablename__ = "sessions"
+
+    id = Column(String, primary_key=True)
+    user_id = Column(String, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+    token = Column(String, unique=True, index=True, nullable=False)
+    expires_at = Column(DateTime(timezone=True), nullable=False)
+    is_active = Column(Boolean, default=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())
+
+    user = relationship("User", back_populates="sessions")