Record the paper-preview pull requests on the task card

Why: The task card is the main record and still had a placeholder where the pull request link belongs.
Evidence: Dev pull request 196, UI pull request 35, frontend pull request 44.
Impact: Task record only. No code or gitlink change.
Refs: feature/docx-paper-preview
Co-authored-by: Cursor <cursoragent@cursor.com>

.task/feature-docx-paper-preview.md

@@ -1,6 +1,6 @@
 # feature/docx-paper-preview 任务卡
 
-任务主记录：<PR 链接，推送后回填>；状态：进行中；owner：weichen
+任务主记录：https://git-home.u1680832.nyat.app:30319/weichen/Agent-System-Dev/pulls/196 ；状态：进行中；owner：weichen
 
 ## 基线与授权