feat(accounts): remove a specific account from the switcher

The switcher only offered 'sign out of active' and 'sign out of all' — no
way to drop a single non-active account (e.g. one stuck in an error state you
can't switch into to sign out). Add a hover × on non-active, non-default rows
and a removeAccount(id) auth action that tears down the client, drops it from
the registry, and clears its per-slot session/token cookies.

Stacks on the switcher redesign in #517.

locales/es/common.json

@@ -138,7 +138,9 @@
     "scheduled": "Programados",
     "unified_all_unread": "Todo no leído",
     "unified_all_starred": "Todo destacado",
-    "unified_all_mail": "Todo el correo"
+    "unified_all_mail": "Todo el correo",
+    "remove_account": "Remove account",
+    "remove_account_confirm": "Remove {account} from this device? You can add it back later."
   },
   "protocol_handlers": {
     "title": "Aplicaciones predeterminadas",