appeals: crosspost appeals to deletion appeal thread.

Crosspost pending appeals to the deletion appeal thread. We do this once
per hour so we can batch together multiple appeals into one post.

app/logical/danbooru_maintenance.rb

@@ -4,6 +4,7 @@ module DanbooruMaintenance
   def hourly
     safely { Upload.prune! }
     safely { PostPruner.prune! }
+    safely { PostAppealForumUpdater.update_forum! }
     safely { regenerate_post_counts! }
   end
 

app/logical/post_appeal_forum_updater.rb

@@ -0,0 +1,26 @@
+module PostAppealForumUpdater
+  APPEAL_TOPIC_TITLE = "Deletion appeal thread"
+
+  def self.update_forum!
+    return if pending_appeals.empty?
+
+    CurrentUser.scoped(User.system) do
+      topic = ForumTopic.order(:id).create_with(creator: User.system).find_or_create_by!(title: APPEAL_TOPIC_TITLE)
+      ForumPost.create!(creator: User.system, topic: topic, body: forum_post_body)
+    end
+  end
+
+  def self.pending_appeals
+    PostAppeal.pending.where(created_at: (1.hour.ago..Time.zone.now)).order(post_id: :asc)
+  end
+
+  def self.forum_post_body
+    pending_appeals.map do |appeal|
+      if appeal.reason.present?
+        "post ##{appeal.post_id}: #{appeal.reason}"
+      else
+        "post ##{appeal.post_id}"
+      end
+    end.join("\n")
+  end
+end