fix(cloud-agent): 布局工具参数错误按字段归类，审批卡补整理徽标

- canvas_arrange_nodes 的参数契约错误改用上游既有的 cloudAgentFieldError：
  snapshotHash 缺失按 required、mode/align/gap/nodeIds/groups 非法按 invalid_value、
  nodeIds/groups 超限按 item_count。原先一律 BadAuthRequest(*AppError)，按上游运行期的
  errors.As 顺序会走 failCloudAgentAdmission 把整轮判死，模型拿不到可纠正回执。
- 审批卡补 .canvas-agent-approval-operation-arrange_nodes 徽标配色（与新增/修改/连线同一组），
  并补一条前端用例：arrange_nodes 预览项不得被 operation() 当成未知值丢掉。

web/test/agent-approval-presentation.test.ts

@@ -64,6 +64,20 @@ describe("Agent approval presentation", () => {
         expect(JSON.stringify(view)).not.toContain("private");
     });
 
+    it("keeps an arrange_nodes preview item instead of dropping it as an unknown operation", () => {
+        // 未知 operation 会被 operation() 判成 null 并丢掉整条预览项，因此新增的
+        // arrange_nodes 必须同时进联合类型与判据，否则审批卡只剩"生成"这个兜底标签。
+        const view = agentApprovalPresentation({ preview: {
+            kind: "canvas_mutation",
+            title: "确认整理画布",
+            description: "请确认要整理的节点。",
+            items: [{ operation: "arrange_nodes", nodeId: "text-1", nodeTitle: "开场分镜", nodeTypeLabel: "文本", summary: "整理《开场分镜》" }],
+        } });
+        expect(view.items).toHaveLength(1);
+        expect(view.items[0].operation).toBe("arrange_nodes");
+        expect(view.items[0].nodeTitle).toBe("开场分镜");
+    });
+
     it("states when an unknown approval cannot identify a target", () => {
         const view = agentApprovalPresentation({ toolName: "unknown_tool", arguments: {} });
         expect(view.items).toHaveLength(0);