[ai] Add claude plugins folder in the repo, and setup local plugins and marketplace for repo

[TheLarkInn]

• Add https://github.com/flora131/atomic Claude Code plugin as a local plugin under claude-plugins/atomic-workflow-plugin/
• Replace generic template CLAUDE.md with Rush Stack-specific project instructions (monorepo structure, build commands, code conventions, verification steps, progressive disclosure)
• Add .mcp.json with DeepWiki MCP server configuration
• Simplify .claude/settings.json: remove telemetry hook, remove remote marketplace reference, point to local plugin directory instead
• Remove .claude/hooks/telemetry-stop.ts (telemetry tracking hook no longer needed)
• Move all Atomic agents, commands, and skills from .claude/ into the plugin directory structure (claude-plugins/atomic-workflow-plugin/)
• Add specs/ and research/ to .gitignore for Atomic workflow artifacts
• Include example research docs generated by the Atomic workflow (research/docs/)
• This should also be supported by copilot cli as well