Disable some unused Rails features

I noticed when running `rails routes` that there's a lot of routes for
major unused Rails features, like storage. I didn't look deeply enough
into ActiveStorage to know if I was risking accepting arbitrary file
uploads, I just figured, if I disable it (which simplifies the app
footprint anyway), then I can be certain! So, goodbye!

config/application.rb

@@ -1,6 +1,29 @@
 require_relative "boot"
 
-require "rails/all"
+require "rails"
+
+# We disable some components we don't use, to: omit their routes, be confident
+# that there's not e.g. surprise storage happening on the machine, and keep the
+# app footprint smaller.
+#
+# Disabled:
+# - active_storage/engine
+# - active_job/railtie
+# - action_cable/engine
+# - action_mailbox/engine
+# - action_text/engine
+%w(
+  active_record/railtie
+  action_controller/railtie
+  action_view/railtie
+  action_mailer/railtie
+  rails/test_unit/railtie
+).each do |railtie|
+  begin
+    require railtie
+  rescue LoadError
+  end
+end
 
 # Require the gems listed in Gemfile, including any gems
 # you've limited to :test, :development, or :production.

config/environments/development.rb

@@ -34,7 +34,7 @@ Rails.application.configure do
   end
 
   # Store uploaded files on the local file system (see config/storage.yml for options).
-  config.active_storage.service = :local
+  # config.active_storage.service = :local
 
   # Don't care if the mailer can't send.
   config.action_mailer.raise_delivery_errors = false

config/environments/production.rb

@@ -40,7 +40,7 @@ Rails.application.configure do
   # config.action_dispatch.x_sendfile_header = "X-Accel-Redirect" # for NGINX
 
   # Store uploaded files on the local file system (see config/storage.yml for options).
-  config.active_storage.service = :local
+  # config.active_storage.service = :local
 
   # Mount Action Cable outside main process or domain.
   # config.action_cable.mount_path = nil