chore: initialize medical consultation agent demo

backend/app/core/context.py

@@ -0,0 +1,15 @@
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class UserContext:
+    """用户上下文：承载宿主系统传入的 user_id 和入口元数据。"""
+
+    user_id: str
+    tenant_id: str | None = None
+    role: str | None = None
+    class_id: str | None = None
+    entry_scene: str | None = None
+    request_id: str | None = None
+    ip_address: str | None = None
+    user_agent: str | None = None