Adds a per-session pending-question badge to sidebar rows, driven by the
live directory-store question state through a dedicated per-session
subscription channel so unrelated streaming never re-renders rows.
Collapsed parent rows roll up pending questions of hidden descendants
from their owning directory stores without bootstrapping them. Question
state is cloned on session delete/archive so badges clear when sessions
disappear. Adds the questionChangeCallbacks sync performance counter,
i18n keys for all locales, and unit tests for the subscription channel
and scope selection.
Fixes#2634
Serhii Dziupin
c1ba631964