feat(frontend): my message menu shows when it was read or listened, group readers open in a right panel

frontend/src/lib/components/MessageList.svelte

@@ -363,13 +363,13 @@
     );
   }
 
-  function applyReceipt(readUpTo: number) {
+  function applyReceipt(readUpTo: number, readAt: string) {
     if (ownId === null) {
       return;
     }
     messages = messages.map((m) =>
       m.sender_id === ownId && m.message_id <= readUpTo && !m.read
-        ? { ...m, read: true }
+        ? { ...m, read: true, read_at: readAt }
         : m
     );
   }
@@ -388,7 +388,7 @@
     ) {
       applyDelete(event.message_ids);
     } else if (event.type === "receipt" && event.chat_id === chatId) {
-      applyReceipt(event.read_up_to);
+      applyReceipt(event.read_up_to, event.read_at);
     }
   }