Add Copilot as the 6th converter target, transforming Claude Code plugins
into Copilot's native format: custom agents (.agent.md), agent skills
(SKILL.md), and MCP server configuration JSON.
Component mapping:
- Agents → .github/agents/{name}.agent.md (with Copilot frontmatter)
- Commands → .github/skills/{name}/SKILL.md
- Skills → .github/skills/{name}/ (copied as-is)
- MCP servers → .github/copilot-mcp-config.json
- Hooks → skipped with warning
Also adds `compound sync copilot` support and fixes YAML quoting for
the `*` character in frontmatter serialization.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
