Order conversations by recency and auto-name from first message

Conversations are now returned sorted by most recently updated first.
New conversations are named using the first 100 characters of the
user's initial message instead of a username+timestamp placeholder.

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

blueprints/conversation/__init__.py

@@ -275,7 +275,7 @@ async def create_conversation():
 async def get_all_conversations():
     user_uuid = get_jwt_identity()
     user = await blueprints.users.models.User.get(id=user_uuid)
-    conversations = Conversation.filter(user=user)
+    conversations = Conversation.filter(user=user).order_by("-updated_at")
     serialized_conversations = await PydListConversation.from_queryset(conversations)
 
     return jsonify(serialized_conversations.model_dump())