feat(dashboard): redesign component detail pages with unified viewer components

- Add MarkdownViewer, JsonViewer, SkillExplorer components with Code/Preview toggle, search (Cmd+F), TOC sidebar, and gradient fade expand/collapse
- Add FileTreeSidebar for skill file navigation (starts collapsed)
- Make file tree panel stretch to match content height
- Green download badge with icon on detail pages
- Remove Add to Stack button and sidebar collapse functionality
- Metadata displayed as clickable label pills with modal
- Add marked dependency for client-side markdown rendering

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: davila7

dashboard/package-lock.json

@@ -22,6 +22,7 @@
     "@types/react-dom": "^19.2.3",
     "astro": "^5.17.2",
     "discord-interactions": "^4.4.0",
+    "marked": "^17.0.4",
     "react": "^19.2.4",
     "react-dom": "^19.2.4",
     "tailwindcss": "^4.1.18"