🤖 Add Anthropic Claude Support

[lucaromagnoli]

Description

Extend the library to support Anthropic's Claude API as a second provider.

Tasks

• Research Anthropic API structure
• Implement AnthropicClient class
• Add Claude-specific models and parameters
• Update ClientFactory for multi-provider support
• Add Claude-specific examples
• Update documentation for multi-provider usage

Acceptance Criteria

• Can use Claude API through same interface
• Provider selection works seamlessly
• Claude-specific features are supported
• Examples demonstrate provider switching
• Tests cover both OpenAI and Anthropic

Dependencies

• Requires: Core architecture complete
• Requires: OpenAI implementation stable

Estimate

Priority: Low
Effort: 3-5 days