Add conversation deletion functionality and update HistoryPage

- Implement a new API endpoint for deleting conversations in the backend.
- Enhance the HistoryPage component to include a dropdown menu for conversation actions, allowing users to delete conversations.
- Update the pagination logic to handle conversation removal and improve user experience during deletion.
- Adjust the loading state and error handling for the delete operation, ensuring smooth interaction.

backend/routes/conversations.py

@@ -115,3 +115,16 @@ async def get_conversation(
             for message in messages
         ],
     )
+
+
+@router.delete("/{conversation_id}")
+async def delete_conversation(
+    conversation_id: str,
+    session: AsyncSession = Depends(get_session),
+):
+    conversation = await session.get(ConversationSession, conversation_id)
+    if not conversation:
+        raise HTTPException(404, "对话记录不存在")
+    await session.delete(conversation)
+    await session.commit()
+    return {"ok": True}