The Claude model manifest declares fast-mode support per model, and the
`claude-opus-5` entry was added without `supportsFastMode`. Claude Code
supports fast mode on Opus 5, so the composer and Command Center hid a
toggle the model actually has.
Set the flag. Everything downstream already keys off it:
`claudeManifestModelSupportsFastMode` gates `buildClaudeFeatures`, which
feeds `listFeatures`, the session `features` getter, `setFeature`, and
the `setModel` auto-clear.
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>