Stop stripping namespace prefixes when converting commands to Copilot
skills. `workflows:plan` now becomes `workflows-plan` instead of just
`plan`, avoiding clashes with Copilot's own features in the chat UI.
Also updates slash command references in body text to match:
`/workflows:plan` → `/workflows-plan`.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
