Convert backlog, project-plan, save-doc, youtube-transcriber, and
z-image from skills/ to commands/ so they appear as user-invocable
slash commands with plugin name prefixes.
Update youtube-transcriber: switch default model from gpt-4o-transcribe
to gpt-4o-mini-transcribe (OpenAI's current recommendation, half cost)
and fix cost estimates that were 4-7x too high.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
