Simplify messages_count trigger install and harden ensure!

Require all three SQLite triggers before treating the counter as installed,
drop the schema.rb / dump-rewrite install paths in favor of rake ensure after
schema load, isolate destructive trigger tests, and cover foreign room moves
plus fixture baseline counts.

Co-authored-by: Thomas Klemm <github@tklemm.eu>

lib/tasks/room_messages_count.rake

@@ -1,38 +1,16 @@
-# schema.rb cannot dump SQLite triggers. Reinstall after loads, and re-append
-# Room::MessagesCount.install! after dumps so the call is not lost.
+# schema.rb cannot dump SQLite triggers — reinstall after schema loads.
 namespace :room_messages_count do
   task ensure: :environment do
     ActiveRecord::Base.connection_pool.with_connection do |connection|
-      next unless connection.adapter_name.match?(/sqlite/i)
-
       Room::MessagesCount.ensure!(connection)
     end
   end
-
-  task append_schema_install: :environment do
-    schema = Rails.root.join("db/schema.rb")
-    contents = schema.read
-    marker = "Room::MessagesCount.install!"
-    next if contents.include?(marker)
-
-    contents.sub!(/\nend\n?\z/, <<~RUBY)
-
-      # SQLite triggers are not dumped by schema.rb; keep rooms.messages_count honest after schema:load.
-      #{marker}
-    end
-    RUBY
-    schema.write(contents)
-  end
 end
 
-{
-  "db:schema:load" => "room_messages_count:ensure",
-  "db:test:load_schema" => "room_messages_count:ensure",
-  "db:schema:dump" => "room_messages_count:append_schema_install"
-}.each do |task_name, enhancement|
+%w[db:schema:load db:test:load_schema].each do |task_name|
   next unless Rake::Task.task_defined?(task_name)
 
   Rake::Task[task_name].enhance do
-    Rake::Task[enhancement].invoke
+    Rake::Task["room_messages_count:ensure"].invoke
   end
 end