Move plugin manifest, subagent, and slash command from
coderabbitai/claude-plugin to the root of this repo so a single
source of truth hosts both the multi-agent skills and the Claude
Code plugin. Skill content (skills/autofix, skills/code-review)
is unchanged and already newer than the claude-plugin copies.
Next steps (separate PRs): update marketplace.json in
anthropics/claude-plugins-official to point at this repo, then
archive coderabbitai/claude-plugin.