Model picker should surface when an enterprise-managed default model overrides user selection

Users observe existing chats or new sessions switching to the enterprise-managed default model (e.g., 5.6 Sol) without any UX explanation. This feels like a bug and erodes trust in model selection.

Observed: Model silently switches to the managed default (Auto or 5.6 Sol) for new sessions; model picker is not sticky and no explanation is shown.

Expected: The UI should clearly indicate when a model is being enforced by enterprise-managed settings and why (banner, tooltip, or model-picker badge).

No file, test, or entry point is named. Start by locating the model picker and the enterprise-managed default-model handling, then trace how new sessions select a model. Done means the UI explains when enterprise settings enforce the model and why, using an appropriate banner, tooltip, or picker badge, with coverage for the reported switching behavior.

Written by the indexing model from the issue text.