feat: Add Mistral AI as new model provider

[brauliolomeli]

Relates to

N/A - New feature addition

Risks

Low - Adding a new model provider with established SDK integration patterns.

• Risk areas: Text generation integration
• Mitigation: Following existing provider integration patterns and thorough testing

Background

What does this PR do?

• Adds Mistral AI as a new model provider
• Integrates Mistral's API using @ai-sdk/mistral package
• Configures environment variables for Mistral model selection
• Implements text generation and object generation handlers for Mistral models
• Sets up default model configurations with sensible parameters
• Adds proper type definitions and model enums

What kind of change is this?

Features (non-breaking change which adds functionality)

• Adds new model provider without affecting existing functionality
• Follows established patterns for model integration

Documentation changes needed?

My changes require a change to the project documentation.

• Added Mistral to ModelProviderName enum in fine-tuning docs
• Environment variable documentation updated in .env.example

Testing

Where should a reviewer start?

1. Review model configuration in packages/core/models.ts
2. Check text generation implementation in packages/core/generation.ts
3. Verify environment variable setup in .env.example

Detailed testing steps

1. Add Mistral API key to environment variables
2. Configure desired model (small/medium/large) in environment
3. Test text generation with Mistral provider
4. Verify proper error handling and response parsing
5. Test with different temperature and token settings
6. Verify model fallback behavior works as expected

Deploy Notes

• New environment variables need to be configured for Mistral integration
• Requires @ai-sdk/mistral package installation

Discord username

bromel