Add docs browser for in-app markdown viewing

[alari76]

Summary

• Adds a lightweight docs browser that lets users browse and read rendered markdown files from any connected repo directly in the terminal UI
• Markdown is rendered with full GFM support (tables, code blocks with syntax highlighting, task lists) using marked + highlight.js, sanitized via DOMPurify
• Entry point is a doc icon on each repo row in the sidebar; clicking opens a file picker, then selecting a file replaces the chat area with the rendered doc
• Input bar remains functional in doc view, with doc context automatically included when messaging Claude

New files

File	Purpose
server/docs-routes.ts	REST API: GET /api/repos/:repoId/docs (file list) and GET /api/repos/:repoId/docs/:filePath (content)
src/hooks/useDocsBrowser.ts	Client state: file picker, content loading, raw/rendered toggle
src/components/MarkdownRenderer.tsx	marked + DOMPurify + highlight.js wrapper
src/components/DocsFilePicker.tsx	Dropdown file list with pinned files (CLAUDE.md, README.md)
src/components/DocsBrowser.tsx	Full doc view with nav bar, back button, raw toggle

Modified files

• RepoSection.tsx — doc icon button on repo row
• LeftSidebar.tsx — prop passthrough
• App.tsx — docs browser integration (replaces chat area when active)
• InputBar.tsx — optional placeholder prop
• ws-server.ts — mount docs routes
• index.css — .docs-prose scoped styles

Test plan

• Click doc icon on a repo row → file picker appears with .md files
• Pinned files (CLAUDE.md, README.md) appear at top with divider
• Select a file → rendered markdown replaces chat area
• Toggle Raw/Rendered button switches between views
• Back button returns to chat
• Escape closes doc view
• Clicking a session in sidebar closes doc view
• Input bar shows custom placeholder in doc mode
• Sending a message while viewing a doc includes file context
• Path traversal attempts return 404
• Light mode styling works correctly

🤖 Generated with Claude Code