Fix: Prioritize user-defined embed models over Transformers.js built-in

[PhilipAD]

Description

When defining an embed model with roles: [embed] in the YAML config file, the extension defaults to using the built-in Transformers.js embedder instead of the user-defined model. This PR fixes this issue by ensuring user-configured embed models in config.yaml are prioritized over the built-in Transformers.js model.

Changes Made

1. Updated core/config/yaml/loadYaml.ts to:
   • Only add the Transformers.js embedder when no other embed models exist
   • Explicitly initialize the selected embed model to prioritize non-Transformers.js models
2. Enhanced core/config/selectedModels.ts to prioritize non-Transformers.js models when selecting the initial embed model

Testing

I've tested these changes with a custom OpenAI-compatible embed model defined in config.yaml with roles: [embed], and confirmed that:

• The custom model is now automatically selected on startup
• The built-in Transformers.js model is still available as a fallback
• The changes don't affect other model roles

Checklist

• [x] I've read the contributing guide
• [x] The relevant docs, if any, have been updated or created
• [x] The relevant tests, if any, have been updated or created