Resolve t2 usernames after every delta sync

enrichUsernames() was only invoked once at startup, so any rooms that
arrived via a later delta /sync stayed pinned to their raw t2_xxx
identifier — which the dashboard then rendered as a bare Matrix-style
ID. Call enrichUsernames() at the tail of syncOnce so new rooms get
resolved to real Reddit usernames before the UI reads them.

Also pass the unformatted username to openConversation() and format
the modal title in the frontend, so lookups by username keep working
after the display sanitisation.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

public/index.html

@@ -2994,7 +2994,7 @@
           const displayName = display === 'unknown' ? 'unknown' : 'u/' + escapeHtml(display);
           const initial = display.charAt(0).toUpperCase() || '?';
           return `
-          <div class="chat-item ${chat.unread ? 'unread' : ''}" style="cursor: pointer;" onclick="openConversation('${escapeHtml(display)}')">
+          <div class="chat-item ${chat.unread ? 'unread' : ''}" style="cursor: pointer;" onclick="openConversation('${escapeHtml(chat.username)}')">
             <div class="chat-avatar">${initial}</div>
             <div class="chat-content">
               <div class="chat-header">
@@ -3418,7 +3418,7 @@
         const statusBadge = hasReply ? '<span class="reply-indicator">Got Reply!</span>' : '';
 
         return `
-        <div class="${cardClass}" onclick="openConversation('${escapeHtml(display)}')">
+        <div class="${cardClass}" onclick="openConversation('${escapeHtml(conv.username)}')">
           <div class="chat-avatar">${initial}</div>
           <div class="chat-content">
             <div class="chat-header">
@@ -3444,7 +3444,7 @@
       const modalBody = document.getElementById('modal-body');
 
       openConversationUsername = username;
-      modalTitle.textContent = `Conversation with u/${username}`;
+      modalTitle.textContent = `Conversation with u/${formatUsernameRaw(username)}`;
       // If a sync is in flight, set a clearer placeholder up front instead of bare "Loading…".
       let placeholderText = 'Loading…';
       try {

src/services/chat/service.ts

@@ -659,6 +659,9 @@ export class ChatService {
     this.cache.set(merged);
     this.cache.markDeltaSync();
     await this.cache.save(merged);
+    // Resolve any t2_-prefixed usernames the delta just introduced, so the
+    // dashboard doesn't show raw Matrix-style IDs for new rooms.
+    await this.enrichUsernames();
     return merged;
   }