fix(skills): harden rename to managed roots and cover failures

Restrict in-place skill rename to managed skill directories, require
frontmatter name to match before moving, roll back/reject with tests,
hide rename in the UI for unmanaged paths, and drop unused toast keys.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/lib/i18n/messages/ja.settings.ts

@@ -718,8 +718,6 @@ export const settingsDict = {
   'settings.skills.sidebar.toast.skillDeleted': 'Skill "{name}" を削除しました',
   'settings.skills.sidebar.toast.deleteSkillFailed': 'Skill の削除に失敗しました',
   'settings.skills.sidebar.toast.duplicateLoadFailed': '複製用の Skill 詳細の読み込みに失敗しました',
-  'settings.skills.sidebar.toast.renameLoadFailed': 'Skill 詳細の読み込みに失敗しました',
-  'settings.skills.sidebar.toast.removeOldAfterRenameFailed': '名前変更後に古い Skill の削除に失敗しました',
   'settings.skills.sidebar.toast.renameFailed': 'Skill の名前変更に失敗しました',
   'settings.skills.sidebar.toast.skillRenamed': 'Skill の名前を「{name}」に変更しました',
   'settings.skills.sidebar.deleteDialog.title': 'Skill を削除',