Refactor gpu-remoting config loading and ignore local artifacts

[Reggie1314129]

Summary

This PR centralizes runtime configuration loading for gpu-remoting and cleans up repository hygiene.

What changed

• add a shared runtime config helper
• replace repeated config.json reads with a common loader
• switch scheduler job metadata loading from an absolute path to a repo-relative path
• ignore local macOS/Python cache artifacts in .gitignore

Why

This reduces duplicated config logic, removes environment-specific path assumptions, and makes the codebase easier to maintain before the next round of refactoring.

Validation

• python3 -m py_compile on updated Python files