Docs: choosing a model, an enabled model is not necessarily usable #515

getting-started's "Choosing a model" picks Models.FirstOrDefault(m => m.Enabled). An enabled model can belong to a provider account that cannot serve turns: an app landed on a model whose account had no balance (402 provider.quota).

Proposed: check how upstream's own client picks a model when none is named (the configured default, a recent model, or the provider default) and recommend that path in the guide.

Source: internal developer-experience evaluation of the 2.0.32 nightly, 2026-10-18 (finding D32-19).