feat(dashboard): 大屏绘制智能体独立页面（按 taskId 存取，不分权）

- 新增带导航+侧边栏的独立页面 DashboardAgentPage：按 taskId 取/存会话，
  有有效 report-json 直显大屏(DashboardApp)，否则进生成过程(不自动跳)+输入框可改
- 后端 dashboard_sessions 存储(model/sql/__init__)+路由/by-task(GET/PUT 不分权)
  + deps/app/models 接线；新表靠 create_all 建，无迁移
- 扩展 useStep3Dashboard：buildInitialPrompt(输入任务JSON) + hydrateTranscript(恢复聊天记录)
- 抽出共享 DashboardChatPanel；report-template 增 buildDashboardPromptFromJson
- 输入 seam core/auth/dashboard-input：JSON 接口未就绪先用占位/演示数据兜底
- 路由 StrategyRoutes dashboard-agent + 侧边栏「问答管理→大屏绘制」
- 圆桌业务链卡片「关系图」改横向布局
- 顺带提交：AIWritingContext 登录切换处理、thread-access-error helper

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

frontend-web/src/pages/StrategyRoutes.tsx

@@ -20,6 +20,7 @@ import { ActionAnalyzes } from "@/strategy-components/components/task-components
 import KnowledgeBaseResourceManagement from "@/strategy-components/components/resource-management/KnowledgeBaseResourceManagement";
 import NetworkActorResourceManagement from "@/strategy-components/components/resource-management/NetworkActorResourceManagement";
 import RoundtablePlanningPage from "@/roundtable-planning/pages/RoundtablePlanningPage";
+import DashboardAgentPage from "@/roundtable-planning/pages/DashboardAgentPage";
 import BusinessChainListPage from "@/roundtable-planning/pages/BusinessChainListPage";
 import BusinessChainEditorPage from "@/roundtable-planning/pages/BusinessChainEditorPage";
 import "@/roundtable-planning/styles/roundtable-planning.css";
@@ -99,6 +100,16 @@ export default function StrategyRoutes() {
               }
             />
 
+            {/* 大屏绘制智能体独立页面（按 taskId 存取；ChatRuntime 提供 ArtifactsProvider 给沙箱预览） */}
+            <Route
+              path="dashboard-agent"
+              element={
+                <ChatRuntime>
+                  <DashboardAgentPage />
+                </ChatRuntime>
+              }
+            />
+
             {/* 需求 0616 #3/#4：zzJC / zzXD 「按类型聚合」模块页（重做，独立路由）。 */}
             <Route path="qa/zzjc/*" element={<AgentModuleRoutes module={AGENT_MODULES.zzjc} />} />
             <Route path="qa/zzxd/*" element={<AgentModuleRoutes module={AGENT_MODULES.zzxd} />} />