Refresh provider support for current AI models

[nang-dev]

Summary

• Add GPT-5.5/GPT-5.4 native OpenAI model support, including Pro/Mini/Nano registry metadata
• Route GPT-5.5 Pro and GPT-5.4 Pro through the Responses API path with reasoning metadata
• Update Anthropic, Gemini, DeepSeek, and Mistral defaults/registries; omit Claude sampling params where required
• Update DeepSeek V4 max output metadata

Verification

• npx prettier --write on touched files
• git diff --check
• npm run check-types:extension: model/provider files pass; remaining failures are existing TerminalProcessExec test mock and MCP response type issues outside this change.