feat: add system tools and state updates

backend/models.py

@@ -114,6 +114,8 @@ class AssistantConfig(BaseModel):
     # every item in ``tools``.
     tools: list[RuntimeTool] = Field(default_factory=list)
     llm_tool_ids: list[str] | None = None
+    # 助手级系统工具仅供 Prompt Pipeline；Workflow 在 Agent 节点中配置。
+    system_tools: list[str] = Field(default_factory=list)
     knowledge_base_id: str | None = None
     knowledge_base_name: str = ""
     knowledge_base_description: str = ""