feat(imitation): add article imitation create flow

Introduce 仿写创作: new list and create views, backend imitation service
and prompt templates, worker task routing for imitation jobs, and one-click
rewrite triggers from question citation sources. Surface source article
URL/title on article list/detail, and restrict failed articles to delete-only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/admin-web/src/lib/errors.ts

@@ -29,7 +29,7 @@ const errorMessageMap: Record<string, string> = {
   article_generating: "文章仍在生成中",
   article_not_editable: "只有已完成文章才可编辑",
   article_lookup_failed: "文章状态读取失败",
-  draft_not_editable: "只有草稿或生成失败的文章才可继续在向导中编辑",
+  draft_not_editable: "只有草稿文章才可继续在向导中编辑",
   article_title_required: "请输入文章标题",
   invalid_image: "请选择图片文件",
   image_upload_too_large: "图片不能超过 10MB",