Add MiniMax-M2.7 and M2.7-highspeed to _PROVIDER_MODELS for minimax
and minimax-cn providers in main.py so hermes model shows them.
Update opencode-go bare ID from m2.5 to m2.7 in models.py.
Salvaged from PR #4197 by octo-patch.
Remove 50 lines of unreachable duplicate model selection logic in
setup_model_provider() for zai/kimi-coding/minimax/minimax-cn providers.
The code referenced undefined `is_coding_plan` variable, crashing setup.
_setup_provider_model_selection() already handles these providers correctly
via _DEFAULT_PROVIDER_MODELS dict.