fix(desktop): polish Models page — ProvidersPanel

Sub-issue of #1303, deferred until #1339 landed (ProvidersPanel was being reshaped by #1340).

• Models — ProvidersPanel.tsx — story Models + Product/Settings/Providers/*

The panel gained three custom-relay catalog entries and an auto-fetch-models flow in #1340; the audit should cover the new states (relay entries in Recommended, the full provider form, post-creation model list) alongside the usual paper cuts. Story variants for states #1340 introduced are expected deliverables. Scope and acceptance criteria: see #1303.