fix: preserve model configuration fallback

[IPollo-1]

What changed

We found a small regression in the model picker refactor that landed with the combined model and reasoning menu. When a ModelSelect caller does not provide its optional onConfigureModels handler, the wrapper still supplies an empty callback to ModelListContent. That prevents the shared list from dispatching our normal openModelPickerEvent, so Configure models can silently do nothing.

This keeps the popover close behavior and explicitly dispatches the existing fallback event when there is no custom handler.

How we checked it

• Compared eva with main; the branch adds one commit and changes only apps/app/src/components/model-select.tsx.
• Verified the updated eva source retains the custom callback path and restores the default event path.
• The local checkout was unavailable to this automation run, so we could not run the Bun test suite here.

Reproduction

1. Render ModelSelect without onConfigureModels.
2. Open the picker and choose Configure models.
3. Before this fix, the popover closes but no model configuration UI opens.
4. With this fix, the existing openModelPickerEvent is dispatched.