fix(security): harden uploads and wecom binding

backend/app/models/wecom_bind_token.py

@@ -0,0 +1,18 @@
+from datetime import datetime
+
+from sqlalchemy import DateTime, String, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.database import Base
+
+
+class WecomBindToken(Base):
+    """A single-use, expiring binding token issued after a verified WeCom callback."""
+
+    __tablename__ = "wecom_bind_tokens"
+
+    token: Mapped[str] = mapped_column(String(64), primary_key=True)
+    wecom_userid: Mapped[str] = mapped_column(String(100), index=True)
+    expires_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), index=True)
+    consumed_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())