feat: add custom base URL configuration support

[hongkongkiwi]

Summary

This PR adds support for configuring custom API base URLs, allowing users to use alternative Groq-compatible endpoints for proxies, local development, or alternative services.

Changes

Core Features

• ✨ Add --base-url CLI argument to set custom API endpoints
• 📝 Add groqBaseUrl field support in ~/.groq/local-settings.json config file
• 🔧 Integrate with Groq SDK's native GROQ_BASE_URL environment variable support
• ✅ Add comprehensive test suite for base URL configuration

Implementation Details

The implementation leverages the Groq SDK's native support for GROQ_BASE_URL environment variable while adding convenient config file support as a fallback, exactly mirroring how API keys are handled.

Priority order (same as API key):

1. Environment variable (GROQ_BASE_URL) - handled natively by SDK
2. Config file (groqBaseUrl) - our fallback when env var not set
3. CLI argument (--base-url) - sets the environment variable

Files Changed

• src/core/agent.ts - Check config file for base URL when creating Groq client
• src/core/cli.ts - Add --base-url CLI option
• src/utils/local-settings.ts - Add groqBaseUrl field and getter/setter methods
• src/tests/base-url.test.ts - Comprehensive test coverage
• README.md - Documentation for the new feature

Testing

All tests pass ✅

npm run build
npx ava src/tests/base-url.test.ts

8 test cases covering:

• CLI argument parsing
• Environment variable handling
• Config file storage and retrieval
• Priority order verification
• URL validation

Usage Examples

# Via CLI argument
groq --base-url https://custom-api.example.com

# Via environment variable
export GROQ_BASE_URL=https://custom-api.example.com
groq

# Via config file (~/.groq/local-settings.json)
{
  "groqApiKey": "...",
  "groqBaseUrl": "https://custom-api.example.com"
}

Benefits

• 🌐 Support for proxy configurations
• 🏠 Local development with custom endpoints
• 🔄 Alternative Groq-compatible services
• 🎯 Consistent with existing API key configuration pattern

[benank]

Nice work! This is a very useful feature.