Admin star on DM message bubbles from admin peers

Extend the admin star to per-message avatars: incoming bubbles from an
admin peer now show the gold star. MessageBubble gains an opt-in adminId
and wraps its avatar img in a non-clipped shell only when the author is an
admin (non-admin bubbles keep the bare <img>). MessageThread passes the
peer pubkey for incoming bubbles; outgoing bubbles are the current user,
whose admin status is already shown on the profile button.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

css/tailwind.source.css

@@ -5896,6 +5896,14 @@
     border: var(--border-width-hairline) solid var(--border-subtle);
   }
 
+  /* Non-clipped relative shell used only when a message avatar needs an admin
+     star; the plain .dm-message-avatar img has no wrapper otherwise. */
+  .dm-message-avatar-wrap {
+    position: relative;
+    display: inline-flex;
+    flex-shrink: 0;
+  }
+
   .dm-message-bubble {
     max-width: 75%;
     display: flex;