Default model not visible in model selector after switching #23247

Bug Report

When the default model (auto-selected via providers.default()) is not the latest in its family, it is hidden from the model selector list. The model appears as the current selection, but switching to another model makes it impossible to switch back.

Steps to Reproduce

1. Configure a provider where the default model has a valid release_date but is not the latest in its family (e.g., zai-coding-plan/glm-5.1 where glm-5-turbo is newer)
2. Open the web UI — the default model is shown as current
3. Open the model selector — the default model is not in the list
4. Switch to a different model
5. Try to switch back — cannot find the default model

Root Cause

models.tsx visible() hides models with valid release dates that are not the latest in their family by default. local.tsx only auto-marks the configured model (from opencode.json) as visible, but not the default model from providers.default().