圆桌第三步流程图模式 + 后台 DAG 任务编排

- 方案总结报告：用户要求结构化输出/流程图时跳过 md 直出 flow-json 流程图，
  报告用文字展示；报告与流程图均可多轮修改、互相切换（detectFlowIntent 识别意图）
- 流程图画布放右侧沙箱位（sidePanel 插槽）不覆盖消息列表，可与 md 预览切换；
  节点随容器宽度自适应缩放并 fitView 居中
- 后台挂起支持真 DAG 编排（分层并行/阶段目标/总控提示词），新增
  orchestration_plan 持久化列 + 迁移；大弹窗流程图按 DAG 分层渲染

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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

@@ -65,6 +65,7 @@ function mapJob(raw: Record<string, unknown>): RoundtableJob {
     pendingClarification: (raw.pendingClarification as string | null) ?? null,
     orchestrationMode: (raw.orchestrationMode as RoundtableJob["orchestrationMode"]) ?? "recommend",
     chain: (raw.chain as RoundtableJob["chain"]) ?? null,
+    orchestrationPlan: (raw.orchestrationPlan as RoundtableJob["orchestrationPlan"]) ?? null,
     error: (raw.error as string | null) ?? null,
     dialogues: Array.isArray(raw.dialogues) ? (raw.dialogues as JobDialogue[]) : [],
     step3: (raw.step3 as RoundtableJob["step3"]) ?? null,
@@ -81,6 +82,7 @@ function toStartBody(p: StartJobPayload) {
     model: p.model,
     orchestrationMode: p.orchestrationMode ?? "recommend",
     chain: p.chain ?? null,
+    orchestrationPlan: p.orchestrationPlan ?? null,
     seedMessage: p.seedMessage,
     threadIds: p.threadIds ?? null,
     coordinatorName: p.coordinatorName ?? "roundtable-coordinator",