feat(libs): create library by name only; root_path derived server-side as BOOKS_DIR/SafeName(name), validated at creation; drop root_path input from admin UI; align changelogs to bilingual template; trim AGENTS.md to rules not derivable from repo layout

docs/CHANGELOG_web.md

@@ -1,7 +1,16 @@
-# Changelog (WebUI)
+# Changelog (WebUI) / 更新日志
 
-All WebUI user-visible changes. Newest version on top.
+All notable WebUI user-visible changes should be documented in this file, newest version on top.
+本文件记录所有 WebUI 的重要用户可见变更，最新版本在最上方。
+
+The format loosely follows Keep a Changelog and can be adapted to the team's habits.
+本文档参考了 Keep a Changelog 的思路，也可以根据团队习惯调整。
 
 ## [Unreleased]
 
+### Changed / 变更
+
+- Creating a library on the admin Libraries page no longer asks for a server-side absolute path; just a name (the directory lands at `BOOKS_DIR/<name>` automatically).
+- 库管理页建库不再要求填写服务端绝对路径，只需库名（目录自动落在 `BOOKS_DIR/<库名>` 下）。
+
 _No WebUI user-visible changes in this release; the structural refactor (`web/` → `frontend/`) does not affect the served app._