feat: unread message tracking with blue dot indicator

Add ContactThreadRead model to track when users last viewed each contact thread.
Contacts with messages newer than the last read time show a blue dot in the sidebar.
Opening a thread automatically marks it as read via markThreadRead mutation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/app/components/workspace/CrmWorkspaceApp.vue

@@ -108,6 +108,7 @@ const {
   avatarSrcForThread,
   markAvatarBroken,
   contactInitials,
+  markContactRead,
   refetchContacts,
 } = useContacts({ apolloAuthReady });
 
@@ -484,6 +485,7 @@ const commThreads = computed(() => {
         channels,
         lastAt: c.lastContactAt,
         lastText: c.lastMessageText || "No messages yet",
+        hasUnread: c.hasUnread,
         items: [] as CommItem[],
       };
     })
@@ -660,11 +662,12 @@ const { crmRealtimeState, startCrmRealtime, stopCrmRealtime } = useCrmRealtime({
     await Promise.all([refetchAllCrmQueries(), loadTelegramConnectStatus()]);
   },
   onNewMessage: (msg) => {
-    // If the message is for the currently open thread → refresh its timeline
+    // If the message is for the currently open thread → refresh its timeline + mark read
     if (msg.contactId === selectedCommThreadId.value) {
       void refreshSelectedClientTimeline(selectedCommThreadId.value);
+      markContactRead(msg.contactId);
     }
-    // Refresh contacts to update sidebar preview (lastMessageText, lastAt)
+    // Refresh contacts to update sidebar preview (lastMessageText, lastAt, hasUnread)
     void refetchContacts();
   },
 });
@@ -1160,6 +1163,7 @@ watch(selectedCommThreadId, () => {
     clientTimelineItems.value = [];
     return;
   }
+  markContactRead(selectedCommThreadId.value);
   void refreshSelectedClientTimeline(selectedCommThreadId.value).catch(() => undefined);
 });