Get Anthropic default model from config if available

[MattMorgis]

I had this in my mcp_agent.config.yaml but my logs still indicated claude-3-5

# mcp_agent.config.yaml
anthropic:
  default_model: "claude-3-7-sonnet-latest"

[saqadri]

Thank you for the fix @MattMorgis! I literally noticed this yesterday and had a fix in a private branch, so thanks for fixing :). Just requested a change to make it more robust (in the case that anthropic settings are defined but not default_model is specified, then it should still default to claude-3.7

[saqadri]

Amazing, thank you!!