💰 fix: Load app config in set-balance script to respect balance settings

[ucodia]

Summary

The npm run set-balance command always errored with Error: Balance is not enabled. Use librechat.yaml to enable it even when balance was correctly configured in librechat.yaml.

Root cause: config/set-balance.js called getBalanceConfig() without the app config argument, so it couldn't read balance settings. The sibling config/add-balance.js script already does this correctly by loading the app config first and passing it in.

This PR aligns set-balance.js with add-balance.js:

• Imports getAppConfig from ~/server/services/Config
• Awaits getAppConfig() before checking balance config
• Passes the resolved appConfig into getBalanceConfig(appConfig)

Fixes #12413 and #12412

Change Type

• Bug fix (non-breaking change which fixes an issue)

Testing

Verified against a locally built Docker image:

1. Build the image locally from this branch.
2. Configure balance in librechat.yaml:

   balance:
     enabled: true
     startBalance: 50000

3. Run npm run set-balance <email> <amount> inside the container.
4. Before the fix: the script exits with Error: Balance is not enabled. Use librechat.yaml to enable it.
5. After the fix: the script proceeds, locates the user, updates the balance via Balance.findOneAndUpdate, and prints Balance set successfully! along with the new balance.
6. Verified behavior parity with npm run add-balance, which was already working correctly with the same config loading pattern.

Test Configuration:

• Locally built Docker image from this branch
• Node.js v20.19.0
• MongoDB (local)
• librechat.yaml with balance.enabled: true

Checklist

• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• My changes do not introduce new warnings
• Local unit tests pass with my changes