users: delete accounts with invalid names.

Add a fix script to delete all accounts with invalid usernames. Also
change it so the owner-level user can delete accounts belonging to other
users.

Users who have logged in in the last year and who have a valid email
address will be given a one week warning. After that all accounts with
invalid names will be deleted. Anyone who has visited the site in the
last 6 months will have already seen a warning page that their name must
be changed to keep using the site.

script/fixes/115_delete_invalid_users.rb

@@ -0,0 +1,57 @@
+#!/usr/bin/env ruby
+
+require_relative "base"
+
+def delete(user)
+  return if !user.name_invalid?
+
+  if ENV.fetch("WARN", "false").truthy? && user.can_receive_email?
+    Dmail.create_automated(to: user, title: "Action required: Change your username or your Danbooru account will be deleted", body: <<~EOS)
+      Your current Danbooru username is invalid. Your Danbooru account will be deleted in one week unless you change your username. Use the link below to change your username:
+
+      * "Change username":/user_name_change_requests/new
+    EOS
+
+    puts "[WARN] id=#{user.id} user='#{user.name}' email='#{user.email_address.address}'"
+  elsif ENV.fetch("DELETE", "false").truthy?
+    UserDeletion.new(user: user, deleter: User.owner).delete!
+    puts "[DELETE] id=#{user.id} user='#{user.name}'"
+  end
+end
+
+with_confirmation do
+  condition = ENV.fetch("COND", "TRUE")
+  users = User.where(Arel.sql(condition))
+
+  users.where("length(name) = 1").find_each do |user|
+    delete(user)
+  end
+
+  users.where("length(name) >= 25").find_each do |user|
+    delete(user)
+  end
+
+  users.where_regex(:name, "[[:space:]]").find_each do |user|
+    delete(user)
+  end
+
+  users.where_regex(:name, "^[[:punct:]]").find_each do |user|
+    delete(user)
+  end
+
+  users.where_regex(:name, "[[:punct:]]$").find_each do |user|
+    delete(user)
+  end
+
+  users.where_regex(:name, "\.(html|json|xml|atom|rss|txt|js|css|csv|png|jpg|jpeg|gif|png|mp4|webm|zip|pdf|exe|sitemap)$").find_each do |user|
+    delete(user)
+  end
+
+  users.where_regex(:name, "[`~!@#$%^&*()+={}\[\]|\\:;'\"<>,?/]").find_each do |user|
+    delete(user)
+  end
+
+  users.where_not_regex(:name, "[[:ascii:]]").find_each do |user|
+    delete(user)
+  end
+end