fix(federation): normalize federated username display across UI

Use parseFederatedUsername() consistently to show base username instead
of raw user@domain format. Replace inline domain text in Username
component with compact globe icon + tooltip. Add globe icons to DM
header and sidebar for federated users.

packages/web/src/components/ui/Username.tsx

@@ -15,13 +15,14 @@ export function Username({ username, showAt, className, style }: UsernameProps)
     return <span className={className} style={style}>{prefix}{username}</span>;
   }
   const name = username.slice(0, atIndex);
-  const domain = username.slice(atIndex + 1);
   return (
-    <Tooltip content={`${prefix}${username}`} position="top">
-      <span className={className} style={style}>
-        {prefix}{name}
-        <span className="text-txt-tertiary text-[0.8em] ml-0.5 font-normal">@{domain}</span>
-      </span>
-    </Tooltip>
+    <span className={`inline-flex items-center gap-0.5 ${className ?? ''}`} style={style}>
+      {prefix}{name}
+      <Tooltip content={`${prefix}${username}`} position="top">
+        <svg width="0.85em" height="0.85em" viewBox="0 0 24 24" fill="currentColor" className="text-txt-tertiary/70 flex-shrink-0 inline-block align-[-0.05em]">
+          <path d="M12 2C6.48 2 2 6.48 2 12s4.48 10 10 10 10-4.48 10-10S17.52 2 12 2zm-1 17.93c-3.95-.49-7-3.85-7-7.93 0-.62.08-1.21.21-1.79L9 15v1c0 1.1.9 2 2 2v1.93zm6.9-2.54c-.26-.81-1-1.39-1.9-1.39h-1v-3c0-.55-.45-1-1-1H8v-2h2c.55 0 1-.45 1-1V7h2c1.1 0 2-.9 2-2v-.41c2.93 1.19 5 4.06 5 7.41 0 2.08-.8 3.97-2.1 5.39z" />
+        </svg>
+      </Tooltip>
+    </span>
   );
 }