fix(users): every user row shows its avatar, not only its initials

System Health's per-user CPU/RAM card asked UserAvatar for the viewer's own
picture with no user id, and the host stats never carried avatarAt, so every
card fell back to letters. The groups now carry avatarAt and the card passes
userId. The user editor's header, the pool board's member chips and the pool
member picker drew hand-made initials; they use UserAvatar too.

server/lib/host-stats.js

@@ -555,12 +555,13 @@ async function usage(t0, t1, p0, p1, mem) {
 
 const round = (n) => Math.round(n * 10) / 10;
 
-/** A user's group fields: id, username and display name (every viewer reads them). */
+/** A user's group fields: id, username, display name and avatar version (every viewer reads them). */
 const userExtra = (u) => ({
   kind: "user",
   userId: u.id,
   username: u.username,
   displayName: u.displayName ?? null,
+  avatarAt: u.avatarAt ?? null,
 });
 
 async function collect() {