refactor: 重构 AgentScope ReAct Runner 与事件处理

- 重构 runtime/runner.py 实现 ReAct Agent 核心逻辑
- 更新事件编码器与存储机制
- 优化 prompt 系统与 tool 调用
- 调整 agent service 与 repository 配合

backend/src/v1/agent/router.py

@@ -128,6 +128,10 @@ async def enqueue_run(
     service: Annotated[AgentService, Depends(get_agent_service)],
     current_user: Annotated[CurrentUser, Depends(get_current_user)],
 ) -> TaskAcceptedResponse:
+    try:
+        request = parse_run_input(request.model_dump(by_alias=True, exclude_none=True))
+    except ValueError as exc:
+        raise HTTPException(status_code=422, detail=str(exc)) from exc
     try:
         validate_run_request_messages_contract(request)
     except ValueError as exc: