The openrouter/auto model is OpenRouter's internal routing feature,
not a callable model. While it's valid as a default (set automatically
during OpenRouter auth flow), showing it in the configure wizard's
model selection causes "Unknown model: openrouter/auto" errors when
users select it manually.
Add a HIDDEN_ROUTER_MODELS set to filter out such internal models
from the selection list while preserving existing functionality.
Fixes#1115
Co-Authored-By: Claude <noreply@anthropic.com>
