Add chat models and scaffold pages/posts apps

Implemented comprehensive models for chat functionality, including Chat, Message, MessageHistory, MessageReaction, and MessageFile. Updated ChatConsumer to enforce authentication and improve message handling. Added initial scaffolding for 'pages' and 'posts' Django apps with basic files.

backend/social/posts/tests.py

@@ -0,0 +1,3 @@
+from django.test import TestCase
+
+# Create your tests here.