feat(shell): enhance slash command completer and menu functionality

CHANGELOG.md

@@ -11,6 +11,7 @@ Only write entries that are worth mentioning to users.
 
 ## Unreleased
 
+- Shell: Redesign slash command completion menu — replace the default completion popup with a full-width custom menu that shows command names and multi-line descriptions, with highlight and scroll support
 - Shell: Fix cancelled shell commands not properly terminating child processes — when a running command is cancelled, the subprocess is now explicitly killed to prevent orphaned processes
 
 ## 1.21.0 (2026-03-12)

docs/en/release-notes/changelog.md

@@ -4,6 +4,7 @@ This page documents the changes in each Kimi Code CLI release.
 
 ## Unreleased
 
+- Shell: Redesign slash command completion menu — replace the default completion popup with a full-width custom menu that shows command names and multi-line descriptions, with highlight and scroll support
 - Shell: Fix cancelled shell commands not properly terminating child processes — when a running command is cancelled, the subprocess is now explicitly killed to prevent orphaned processes
 
 ## 1.21.0 (2026-03-12)

docs/zh/release-notes/changelog.md

@@ -4,6 +4,7 @@
 
 ## 未发布
 
+- Shell：重新设计斜杠命令补全菜单——使用全宽自定义菜单替代默认的补全弹窗，展示命令名称和多行描述，支持高亮和滚动
 - Shell：修复取消的 Shell 命令未正确终止子进程的问题——当运行中的命令被取消时，子进程现在会被显式杀死，防止产生孤儿进程
 
 ## 1.21.0 (2026-03-12)