fix: BYOK models not appearing in chat model picker

[hoyyeva]

Summary

Ollama models are not visible in the chat model pickers with Agent mode. This is because
byokKnownModelToAPIInfo() does not set isUserSelectable: true
on the returned model metadata. VS Code's model picker filters on this field,
so all BYOK models get filtered out.

The similar function chatModelInfoToProviderMetadata() already sets
isUserSelectable: true — this is a one-line consistency fix to
byokKnownModelToAPIInfo().

Steps to reproduce

1. Configure an Ollama provider (or any BYOK provider)
2. Open Copilot Chat and click the model picker dropdown
3. No BYOK models appear

Fix

Add isUserSelectable: true to the model metadata returned by
byokKnownModelToAPIInfo() in src/extension/byok/common/byokProvider.ts.

[Copilot]

Pull request overview

This PR fixes a bug where BYOK (Bring Your Own Key) models, such as Ollama, were not appearing in the chat model picker. The root cause was that byokKnownModelToAPIInfo() was not setting isUserSelectable: true on the returned model metadata, causing VS Code's model picker to filter them out.

Changes:

• Added isUserSelectable: true to model metadata in byokKnownModelToAPIInfo() for consistency with chatModelInfoToProviderMetadata()