feat(roundtable): 会商前端调用报错收集 + 诊断页用户名/范围切换

- 前端调用报错收集（用户实际遇到的报错，服务端诊断看不到的也收）：新增
  POST /api/roundtable-diagnostics/report（非 admin，scope="client"）+ 前端上报器
  roundtable-planning/api/diagnostics-report.ts。streamMultiAgent（第二步席位 +
  第三步报告/结构化/绘制/大屏）覆盖 HTTP 错误(502)、SSE error 帧、worker error 帧
  (模型没调用成功)、fetch 网络不可达、流式中途中断，reported 去重；initMultiAgent /
  intent / recommend / 后台作业接口同步上报。
- 诊断页：每条报错显示上报用户名(👤，user_id→邮箱@前缀，后端 best-effort 解析)；
  第一个筛选改为「后台挂起 / 前台调用」切换（前台调用=foreground,client，后端 scope
  支持逗号多值），阶段下拉随范围联动（后台→二三步；前台→一二三步）。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend-web/src/roundtable-planning/api/roundtable-jobs.ts

@@ -15,6 +15,7 @@ import { apiFetch } from "@/core/api/fetch-client";
 import { getBackendBaseURL } from "@/core/config";
 
 import { getAvatarTypeFor } from "../lib/roundtable-constants";
+import { reportRoundtableError } from "./diagnostics-report";
 import { seatModeToRunParams } from "../lib/seat-mode";
 import {
   isTerminalJobStatus,
@@ -29,6 +30,11 @@ const BASE = () => `${getBackendBaseURL()}/api/roundtable-jobs`;
 async function readJson<T>(res: Response, ctx: string): Promise<T> {
   if (!res.ok) {
     const text = await res.text().catch(() => "");
+    reportRoundtableError({
+      stage: "job", event: "job_api_http_error",
+      message: `后台作业接口「${ctx}」失败 (HTTP ${res.status}): ${text.slice(0, 500)}`,
+      httpStatus: res.status,
+    });
     throw new Error(`${ctx} failed (${res.status}): ${text}`);
   }
   return (await res.json()) as T;
@@ -221,7 +227,13 @@ export function streamJob(jobId: string, handlers: StreamJobHandlers, taskId?: s
             continue;
           }
           if (frame.event === "error") {
-            handlers.onError?.(String(frame.detail ?? "unknown stream error"));
+            const detail = String(frame.detail ?? "unknown stream error");
+            reportRoundtableError({
+              stage: "job", event: "job_stream_error_frame",
+              message: `后台作业进度流报错：${detail.slice(0, 500)}`,
+              jobId, detail: { taskId },
+            });
+            handlers.onError?.(detail);
             continue;
           }
           const job = mapJob(frame);