Slack: an Avatars switch in the transcript's gear

Off, the picture square goes and each row starts at the left edge — the
same behaviour as ProdCom's channel-icon switch.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

modules/slack/style.css

@@ -117,6 +117,8 @@
   user-select: none;
   -webkit-user-select: none;
 }
+/* "Avatars" off: the square goes and the row starts at the left edge, as in ProdCom */
+[data-module="slack"] .sl-wrap.hide-avatars .sl-avatar { display: none; }
 [data-module="slack"] .sl-avatar-img {
   width: 100%;
   height: 100%;