fix(messages): never render raw uid as group sender name (#32)

Senders missing from the member list (left/removed) fell back to msg.from verbatim, and nameless members arrive from the REST API with the uid itself as display_name. Resolve both through a shared groupSenderLabel helper that substitutes a fixed placeholder for uid-shaped names (message bubbles, quoted replies, history search).

web/src/features/messages/MessageBubble.tsx

@@ -9,6 +9,7 @@ import { callResultDisplay, contactCardContentOf, isRecalled, isServerDeleted, s
 import { renderDrafty } from '@/lib/messages/drafty';
 import { formatBubbleTime, formatEventTimestamp } from '@/lib/messages/time';
 import { isFailedStatus, isSendingStatus, outgoingStatusLabel } from '@/lib/messages/status';
+import { groupSenderLabel } from '@/lib/messages/sender-name';
 import { retryMessage } from '@/lib/tinode/send';
 import { ensureTopicAttached } from '@/lib/tinode/topics';
 
@@ -154,12 +155,12 @@ export function MessageRow({
             not navigate away and lose whatever's already been picked. */}
         {isGroup && !mine && !selectMode && msg.from ? (
           <Link to={`/contacts/${msg.from}`} className="flex-none no-underline">
-            <Avatar id={msg.from} name={senderName || msg.from} avatarFileId={avatarFileId} className="h-9 w-9 rounded-lg text-sm" />
+            <Avatar id={msg.from} name={groupSenderLabel(senderName)} avatarFileId={avatarFileId} className="h-9 w-9 rounded-lg text-sm" />
           </Link>
         ) : (
           <Avatar
             id={msg.from || (isGroup ? '' : peerName)}
-            name={mine ? '我' : isGroup ? senderName || msg.from : peerName}
+            name={mine ? '我' : isGroup ? groupSenderLabel(senderName) : peerName}
             avatarFileId={avatarFileId}
             fallbackBgClass={mine ? 'bg-accent' : undefined}
             className="h-9 w-9 flex-none rounded-lg text-sm"
@@ -170,10 +171,10 @@ export function MessageRow({
             <div className={`flex items-center gap-1 px-0.5 text-xs text-text-tertiary-4 ${mine ? 'flex-row-reverse' : ''}`}>
               {!mine && !selectMode && msg.from ? (
                 <Link to={`/contacts/${msg.from}`} className="text-text-tertiary-4 no-underline hover:underline">
-                  {senderName || msg.from}
+                  {groupSenderLabel(senderName)}
                 </Link>
               ) : (
-                <span>{mine ? '我' : senderName || msg.from}</span>
+                <span>{mine ? '我' : groupSenderLabel(senderName)}</span>
               )}
               <MessageRoleTag role={senderRole === 'owner' || senderRole === 'admin' ? senderRole : undefined} />
             </div>