feat: Add OpenAI provider support for AI assistance

Enables using OpenAI-compatible endpoints (OpenAI, Azure OpenAI, OpenRouter,
LiteLLM proxies) as an alternative to Anthropic for AI-powered query assistance.

Adds support for custom headers (X-Client-Id, X-Username) and request body
customization via AI_EXTRA_BODY for proxy/gateway compatibility. Enhances
error logging with detailed API call diagnostics.

Also upgrades sql-formatter to 15.7.0 to address breaking API changes.

Author: vinzee