Release v1.41.5

fix: strip provider prefix from model name for native xAI/OpenAI APIs

When using tiered models (fast/smart), the model names include a provider
prefix (e.g., "xai/grok-code-fast-1") for OpenRouter compatibility. However,
native APIs like xAI don't accept this prefix.

This fix:
1. Strips the provider prefix when calling native APIs (xAI, OpenAI)
2. Preserves the prefix for OpenRouter which requires it
3. Fixes ModelInfo display to avoid double-prefixing (xai/xai/...)
4. Uses the correct endpoint for each provider in tiered requests

Fixes API error: "model xai/grok-code-fast-1 does not exist"