Generalise a measurement in the spec that named an inbox

The end-to-end note for background liveness quoted a real unread count
from a real mailbox. The point it makes is that a background app's count
rises untouched, which it makes just as well without the number.

docs/superpowers/specs/2026-09-01-work-app-design.md

@@ -228,8 +228,8 @@ does:
    tab. It fetches as if you had just looked at it, and keeps its state — unlike a reload,
    which would throw away a half-written reply.
 
-**Measured end to end:** Gmail behind Odoo went from 155 to 157 unread without being
-touched, and the app raised `Gmail / 1 new`.
+**Measured end to end:** with a mail app sitting behind another, its unread count rose on
+its own without the app being touched, and a banner was raised from it.
 
 ### Unread counting