feat: add takeover fields to Authorization model

Add takeover_enabled, takeover_mode, and takeover_delay_seconds columns
to the Authorization model with a SQLite migration, and include them
in to_dict(). Test: test_takeover_model.py.

digital-avatar-app/backend/models.py

@@ -51,6 +51,9 @@ class Authorization(Base):
     target_name = Column(String, default="")
     permissions = Column(JSON, default=list)
     status = Column(String, default="active")  # active | inactive
+    takeover_enabled = Column(Boolean, default=False)  # 是否开启分身接管
+    takeover_mode = Column(String, default="immediate")  # immediate | delayed
+    takeover_delay_seconds = Column(Integer, default=30)  # 延迟秒数
     created_at = Column(DateTime, server_default=func.now())
 
     def to_dict(self):
@@ -62,6 +65,9 @@ class Authorization(Base):
             "targetName": self.target_name,
             "permissions": self.permissions or [],
             "status": self.status,
+            "takeoverEnabled": self.takeover_enabled,
+            "takeoverMode": self.takeover_mode,
+            "takeoverDelaySeconds": self.takeover_delay_seconds,
             "createdAt": _iso(self.created_at),
         }