feat(frontend): 支持 Roundtable 写文件流式预览与消息流聚合展示

功能说明：\n- 为写文件工具链增加流式预览状态模型（in-flight、chunk 归并、已完成）\n- 在消息面板中支持 write_file 流式 artifact 的动态插入/更新与完成态呈现\n- 优化 artifact 详情页的文件名与来源显示，兼容流式生成中文件路径\n- 在 Roundtable 工作流 step2 流程中注入与监听 write_file 事件，支持多阶段消息统一展示\n- 补充单测覆盖：streaming-write-preview、write-file-in-flight、streaming-artifacts 等关键路径

frontend-web/src/pages/AgentChatPage.tsx

@@ -38,6 +38,7 @@ import { TokenUsageIndicator } from "@/components/workspace/token-usage-indicato
 import { Tooltip } from "@/components/workspace/tooltip";
 import { normalizeAgentQuestions, useAgent } from "@/core/agents";
 import { getAPIClient } from "@/core/api";
+import { useTheme } from "@/contexts/ThemeContext";
 import { useI18n } from "@/core/i18n/hooks";
 import { queueLlmWikiConversationDeposit } from "@/core/llmwiki/conversation-deposit";
 import { useModels } from "@/core/models/hooks";
@@ -92,6 +93,8 @@ import type { Message } from "@langchain/langgraph-sdk";
 
 /** 内置「模板数据转换器」agent 的稳定 id。仅此 agent 的对话页显示「页面模板 + 渲染预览」调试入口。 */
 const TEMPLATE_BUILDER_AGENT_ID = "template-json-builder";
+/** 实验性页面研报智能体：发送当前界面明暗模式供其选择同色系 HTML 骨架。 */
+const PAGE_REPORT_DESIGNER_AGENT_ID = "page-report-designer";
 const RWFX_SQ_REPORT_CONTEXT_MAX_CHARS = 12000;
 const RWFX_SQ_REPORT_CONTEXT_TAIL_CHARS = 2000;
 
@@ -226,6 +229,7 @@ export default function AgentChatPage({
 } = {}) {
   const routeBase = useRouteBase();
   const { t } = useI18n();
+  const { baseMode } = useTheme();
   const [showFollowups, setShowFollowups] = useState(false);
   const router = useRouter();
   // 独立智能体页的左列是 AgentChatSidebar，而不是外层 WorkspaceSidebar；
@@ -677,13 +681,18 @@ export default function AgentChatPage({
         settings.context.writing_mode && writingArtifactPath
           ? { writing_artifact_path: writingArtifactPath }
           : {};
+      const pageReportThemeContext =
+        agent_id === PAGE_REPORT_DESIGNER_AGENT_ID
+          ? { presentation_theme: baseMode }
+          : {};
       void sendMessage(threadId, message, {
         ...writingExtraContext,
         ...(extraContext ?? {}),
         agent_id,
+        ...pageReportThemeContext,
       });
     },
-    [sendMessage, threadId, agent_id, settings.context.writing_mode, writingArtifactPath],
+    [sendMessage, threadId, agent_id, settings.context.writing_mode, writingArtifactPath, baseMode],
   );
 
   // 任务流程：切换 / 新建会话时，停掉「上一会话服务端在跑」的 run（老对话要停止）。
@@ -757,9 +766,14 @@ export default function AgentChatPage({
     async (answer: string) => {
       setHasStartedConversation(true);
       await stopActiveThreadBeforeClarificationReply(threadId, thread);
-      await sendMessage(threadId, { text: answer, files: [] }, { agent_id });
+      await sendMessage(threadId, { text: answer, files: [] }, {
+        agent_id,
+        ...(agent_id === PAGE_REPORT_DESIGNER_AGENT_ID
+          ? { presentation_theme: baseMode }
+          : {}),
+      });
     },
-    [sendMessage, thread, threadId, agent_id],
+    [sendMessage, thread, threadId, agent_id, baseMode],
   );
 
   const handleStop = useCallback(async () => {