feat：新增对话历史列表

app/schemas/conversation.py

@@ -25,3 +25,15 @@ class ConversationCreated(BaseModel):
 class ConversationDetail(BaseModel):
     conversation_id: str
     turns: list[Turn]
+
+
+class ConversationSummary(BaseModel):
+    """历史会话列表项，只包含已产生对话的会话"""
+
+    conversation_id: str
+    title: str  # 取自首轮用户输入，过长时截断
+    updated_at: datetime  # 最近一轮对话的创建时间
+
+
+class ConversationList(BaseModel):
+    conversations: list[ConversationSummary]