🔌 ci: Configure Provider Base URLs For Live Tests

[lia-by-librechat]

Summary

• Pass optional OPENAI_BASE_URL and ANTHROPIC_BASE_URL to CI steps that call those providers, sourcing repository variables or secrets. Unset values retain the SDK defaults.
• Verify that both provider wrappers route requests through these environment URLs using an offline, intercepted-fetch test.

CI configuration

Set OPENAI_BASE_URL and/or ANTHROPIC_BASE_URL as repository variables (or secrets) if CI must use a gateway. Keep the corresponding provider API keys configured separately. No workflow change is required when the endpoints are not overridden.

Validation

• Focused Jest routing and OpenAI endpoint-sensitive tests
• TypeScript typecheck, ESLint, Prettier, and CI workflow YAML validation