docs: add OmniRoute provider examples

[diegosouzapw]

Summary

Document OmniRoute in the existing OpenAI-compatible provider examples.

What changed

• Add the OmniRoute local gateway configuration to the English README.
• Add the same configuration to the Chinese README.
• Use CoreCoder's existing OPENAI_API_KEY, OPENAI_BASE_URL, and
  CORECODER_MODEL configuration without introducing provider-specific code.

The documented setup routes CoreCoder through
http://localhost:20128/v1 with the OmniRoute auto model.

Validation

• python -m pytest tests/ -q - 86 passed.
• python -m compileall -q corecoder tests - passed.
• python -m build - passed.
• python -m twine check <temporary-dist>/* - passed for the wheel and sdist.
• git diff --check - passed.
• Sanitized local smoke - confirmed Bearer authentication,
  POST /v1/chat/completions, model: auto, streaming, function tool schemas,
  and streamed tool-call reconstruction.

ruff check corecoder tests continues to report the same 41 pre-existing
violations from the upstream baseline; this documentation-only change does not
add or modify Python code.