Bumps _SOULSYNC_BASE_VERSION to 2.7.4 and refreshes the What's New panel +
version-modal highlight reel to the 2.7.4 set (re-identify #889 headline; #890
title-strip; #891 residual-folder cleanup; #886 AAC tier; #887 Spotify Free
status; #884 NZBGet; #885 tz; Sokhi import-cleanup batch), with 2.7.3 rolled into
the brief 'earlier versions' summary per the current-release-only convention.