[WIP] Build Confluence macro for managing Markdown files

[Copilot]

• Scaffold markdown-mirror/manifest.yml with required scopes and Custom UI macro definition
• Create backend markdown-mirror/src/index.js with fetchMarkdown and saveMarkdown resolvers using Confluence Attachments API
• Create markdown-mirror/package.json (root) for backend dependencies
• Create React frontend in markdown-mirror/static/markdown-editor/ with:
  • package.json with Monaco Editor, markdown-it, github-markdown-css dependencies
  • public/index.html entry point
  • src/index.js React entry point
  • src/App.js with Edit/View modes, Monaco Editor, markdown-it rendering, Copy Raw Markdown, and Empty State
  • src/App.css for styling
• Generate markdown-mirror/Claude.md documentation (deploy steps, permissions, technical overview)
• Update .gitignore to exclude node_modules for the Forge app
• Review and validate all files