Reverts pass-through from the previous commit. Copilot supports a model
field but expects display names ("Claude Opus 4.5"), not Claude model IDs
or bare aliases. Unlike Droid (which natively resolves "sonnet"), Copilot
has no documented resolution for Claude-specific values. Emitting an
unrecognized value is worse than omitting the field (which falls back to
the platform default).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>