When users configure an OpenAI-compatible provider (like OpenRouter) with
a model that doesn't support function calling, they previously saw only a
generic "404" error. This made troubleshooting difficult.
Changes:
- Add FunctionCallingNotSupportedError class with a clear, actionable message
- Detect 404 errors and tool-related error messages when using custom providers
- Update error partial to display the actual error message instead of generic text
- Add i18n support for the error message
Fixes#830https://claude.ai/code/session_01EpuAVyy5qRV4hYjwPELff4