feat(cmd): add API validation tool for quick configuration testing

[salignatmoandal]

What does this PR do?

This PR adds a simple CLI tool (cmd/validate-api/main.go) that allows users to quickly test their OpenAI API configuration without writing any code.

Why is this useful?

• Quick diagnostics: Users can verify their API key and connection in seconds
• Better error messages: Provides actionable guidance for common issues (auth, rate limits, network)
• Developer experience: Helps new contributors and users troubleshoot setup issues
• CI/CD integration: Can be used in scripts to validate configuration before running tests

What's included?

• cmd/validate-api/main.go: Main validation tool (~100 lines)
• Command line options: --api-key, --timeout, --verbose
• Comprehensive error handling with actionable messages
• Integration with existing environment variable support

How to test?

# Basic test
go run cmd/validate-api/main.go

# With options
go run cmd/validate-api/main.go --api-key sk-... --timeout 30s --verbose

# Test error handling (invalid key)
OPENAI_API_KEY=sk-invalid go run cmd/validate-api/main.go

Files changed

• cmd/validate-api/main.go (new)
• README.md (adds validation section)

Impact

• ✅ No breaking changes: Doesn't affect existing API
• ✅ Lightweight: ~100 lines, no external dependencies
• ✅ Testable: Easy to validate manually
• ✅ Maintainable: Simple, focused utility

Related Issues

N/A

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Feel free to open an issue or PR if you have suggestions!