Skill detail no longer has an in-app file browser / preview

What changed

Opening a skill in the library now shows a metadata-only detail dialog. The v1/v2 skill detail page that rendered an expandable file tree with per-file markdown and code preview is removed.

Why this matters to the user

Users who browsed a skill's files and previewed their contents inside the app can no longer do so from the skill detail view — only the skill's metadata is shown.

What the user should do

Open the skill's folder on disk to inspect or edit its files.

Notes for release manager

• Removed surface: pages/library/detail/skill/SkillDetailPage.tsx (+ skillFileTree.tsx); replaced by the metadata-only SkillDetailDialog.tsx.
• Inherited verbatim from feat/chat-page; if the file browser is meant to return, it needs a home in/alongside SkillDetailDialog upstream.