Record the chat timeline task scope

Why: The task card still had placeholders after task-start, so the authorized scope and non-goals were not on the branch.
Evidence: Card now names the approved timeline, artifact card, preview pane, and false-deliverable guard, and excludes merge, production deploy, and history rewrite.
Impact: Documentation only; no runtime change.
Refs: feature/chat-timeline-preview
Co-authored-by: Cursor <cursoragent@cursor.com>

.task/feature-chat-timeline-preview.md

@@ -6,11 +6,12 @@
 
 - 权威仓：ssh://git@git-ssh.u1680832.nyat.app:31411/weichen/Agent-System-Dev.git；目标分支：main；R0（initial_base_sha）= 4adc4cc458f15546e5605dc55843acc26b310c41
 - 工作区：/home/weichen/projects/Agent-System-Dev-wt-feature-chat-timeline-preview（worktree）；分支：feature/chat-timeline-preview
-- 授权与交付终点：<本次允许的动作与终点；未授权事项写明>
+- 授权与交付终点：用户已批准方案并要求按方案实施到提 PR。允许改 Core / Backend / UI / Frontend 与 Dev 仓 DESIGN.md、推进 gitlink、推送 feature/chat-timeline-preview 并建 PR。合入、部署生产、改写历史不在本次授权内。
 
 ## 目标与非目标
 
-<预期结果、受影响入口/模块/契约；明确不做什么。>
+- 目标：助手消息按工作时间线呈现（运行中展开，终轮后折成「已工作 X」）；工件以可点击卡片出现；点击在对话右侧多标签预览区打开（docx 按页面版式）；后端拦截没调用工具却声称已生成文件的终轮回复。
+- 非目标：项目文件目录树；服务端 Office 转 PDF；改右栏收件箱/文件列表的业务。
 
 ## 同步记录