feat: update backlog sync logic to queue requests and adjust response structure

public/index.html

@@ -126,13 +126,13 @@
       el.channelFilter.value = state.selectedTextChannel;
       applyActiveTab(state.activeTab);
       if ((textChanged || textGuildChanged) && state.selectedTextChannel && state.selectedTextGuild) {
-        await apiRequest('/api/backlog-sync', {
+        apiRequest('/api/backlog-sync', {
           method: 'POST',
           body: JSON.stringify({ guildId: state.selectedTextGuild, channelId: state.selectedTextChannel }),
         }).catch((error) => showError(`Backlog sync failed: ${error.message}`));
       }
       if (textChanged || textGuildChanged || state.activeTab === 'text') {
-        await fetchText().catch((error) => showError(error.message));
+        fetchText().catch((error) => showError(error.message));
       }
       await reconcileListenState();
       await reconcileStreamingState();