Session expiry indicator in switcher (optional / lower priority)

[saknarajapakshe]

Part of: #25

What to build

Show a "needs sign-in again" indicator in the switcher for any linked account whose session has expired, and let the user re-enter their password inline (reauthenticate already exists and works).

Done when

• An expired account looks visibly different in the list.
• Re-entering the password fixes it without a page reload.

Depends on

#39. Lowest priority in this project — fine to pick up later.