Implement CivitAI API integration

[Revmagi]

Build complete CivitAI API client with search, model details, and import functionality.

Tasks

• Implement CivitAI API client from API_INTEGRATIONS.md spec
• Add authentication support with API tokens
• Build model search interface
• Implement model detail viewing
• Add model import to database functionality
• Include rate limiting and error handling

Acceptance Criteria

• CivitAI search works with filters
• Model metadata imports correctly
• Authentication with API tokens functional
• Rate limiting prevents API abuse
• Error handling provides clear feedback