Add migration to make post authors follow new threads

Author: trichoplax

db/migrate/20260208223211_follow_own_posts.rb

@@ -0,0 +1,10 @@
+class FollowOwnPosts < ActiveRecord::Migration[7.2]
+  def change
+    to_insert = Post.where.not(post_type_id: [PolicyDoc.post_type_id, HelpDoc.post_type_id])
+                    .where.not(user_id: nil)
+                    .pluck(:id, :user_id)
+                    .map { |post_id, user_id| { post_id: post_id, user_id: user_id } }
+
+    NewThreadFollower.insert_all(to_insert)
+  end
+end