[Feature]: Color-code / label model favorites by account so multi-subscription users can tell them apart

[jameswasher]

Area

apps/desktop

Problem or use case

With multiple provider accounts (e.g. two Claude Max subscriptions, or Claude plus other providers), the favorites rail shows the same model name and logo with no indication of which account each favorite is tied to. The model picker's left rail already shows per-account provider badges (e.g. C-, CL, C-), but the flat favorites list drops that signal — so a favorites list that spans subscriptions is ambiguous.

The whole point of favorites is to pin the best model from each subscription. That's unusable if you can't tell which favorite belongs to which account.

Proposed solution

Carry the account / provider-instance identity onto each favorite row — a color-coded badge, or the same account glyph already used in the picker's left rail — so every favorite is visually attributable to its subscription.

Why this matters

Multi-account / multi-subscription usage is a first-class workflow (see #7547, #6896, #6993). Favorites should be legible across accounts, not just within one.

Contribution

Open to helping test; happy to iterate on the visual treatment.