Fix/provider error labels

[vdalal]

Add provider name to API error messages (rate limits, etc.)

[vdalal]

Provider Name in Error Messages

• Modified src/agent/agent.ts to include the specific LLM provider's name in error messages.
• Specifically, it resolves the provider (resolveProvider(this.model).displayName) and passes it to formatUserFacingError(errorMessage, provider).
• This change helps attribute rate limit errors (and other API errors) to the exact provider being used, making debugging easier when the agent is using multiple providers, optional providers or fallback models.

[virattt]

Thanks!