create follow table: user follows user

app/models/follow.py

@@ -0,0 +1,17 @@
+from sqlalchemy import Column, DateTime, String, ForeignKey, UniqueConstraint
+from sqlalchemy.sql import func
+from .base import AutoID, Base
+
+class Follow(Base, AutoID):
+    """用户关注关系表"""
+    __tablename__ = "follows"
+
+    follower_id = Column(String(32), ForeignKey("users.id", ondelete="CASCADE"), index=True)
+    followee_id = Column(String(32), ForeignKey("users.id", ondelete="CASCADE"), index=True)
+    
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    # 联合唯一索引：防止重复关注
+    __table_args__ = (
+        UniqueConstraint("follower_id", "followee_id", name="uq_follower_followee"),
+    )