Upgrade to Rails 7.1 and apply new framework defaults

* Remove deprecated options from environments
* Remove deprecation warnings for upcoming Rails 7.2
* Dump schema with new defaults
* Remove outdated (and erroneous) data attribute in view
* Resolve a `NoMethodError` for seeds_spec.rb

config/initializers/monkey_patches.rb

@@ -17,3 +17,11 @@ module WillPaginate
     end
   end
 end
+
+# Temporary required for Rails 7.1+ and Slim 5.1+.
+# TODO: No GitHub issue yet
+module ActionView
+  class OutputBuffer
+    alias + concat
+  end
+end