Add a warning when ANTHROPIC_BASE_URL would be set but the active profile's
.credentials.json would override ANTHROPIC_API_KEY with subscription OAuth,
routing requests to Anthropic instead of the intended provider.
Fixes the MiniMax routing issue: use --profile minimax (~/.claude-minimax/,
no stored credentials) for non-Anthropic providers.
Update presets example to use profile: minimax for quick-minimax preset.
63 tests passing.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>