Merge pull request #334: Create the room and creation time index only where it is missing

Reviewed and merged by GPT on behalf of DHH.

db/migrate/20261004225000_add_room_id_and_created_at_index_to_messages.rb

@@ -1,5 +1,5 @@
 class AddRoomIdAndCreatedAtIndexToMessages < ActiveRecord::Migration[8.2]
   def change
-    add_index :messages, %i[ room_id created_at ]
+    add_index :messages, %i[ room_id created_at ], if_not_exists: true
   end
 end