Wrong provider ID 'anthropic' used in MistralConfigForm::submitForm()

Problem/Motivation

In MistralConfigForm::submitForm(), the defaultIfNone() method is called with 'anthropic' as the provider ID instead of 'mistral':

$this->aiProviderManager->defaultIfNone('chat', 'anthropic', 'mistral-large-latest');                                                                                               
  $this->aiProviderManager->defaultIfNone('embeddings', 'anthropic', 'mistral-embed');  

when a user saves the Mistral configuration form and no default provider is set, the system attempts to set Anthropic as the default provider with Mistral model names, which is incorrect.

Steps to reproduce

1. Install Mistral provider module on a fresh site with no default AI providers configured
2. Navigate to /admin/config/ai/providers/mistral
3. Enter an API key and save the form
4. Check the AI settings - the default provider will not be set to Mistral as expected

Proposed resolution

Change the provider ID from 'anthropic' to 'mistral'

Remaining tasks

Fix the provider ID in MistralConfigForm.php