docs: add documentation for various classes in app/logical.

app/logical/current_user.rb

@@ -1,3 +1,15 @@
+# A global variable containing the current user, the current IP address, the
+# current user's country code, and whether safe mode is enabled.
+#
+# The current user is set during a request by {ApplicationController#set_current_user},
+# which calls {SessionLoader#load}. The current user will not be set outside of
+# the request cycle, for example, during background jobs, cron jobs, or on the
+# console. For this reason, code outside of controllers and views, such as
+# models, shouldn't rely on or assume the current user exists.
+#
+# @see https://api.rubyonrails.org/classes/ActiveSupport/CurrentAttributes.html
+# @see ApplicationController#set_current_user
+# @see SessionLoader#load
 class CurrentUser < ActiveSupport::CurrentAttributes
   attribute :user, :ip_addr, :country, :safe_mode
 
@@ -5,6 +17,10 @@ class CurrentUser < ActiveSupport::CurrentAttributes
   delegate :id, to: :user, allow_nil: true
   delegate_missing_to :user
 
+  # Run a block of code as another user.
+  # @param user [User] the user to run as
+  # @param ip_addr [String] the IP address to run as
+  # @yield the block
   def self.scoped(user, ip_addr = "127.0.0.1", &block)
     set(user: user, ip_addr: ip_addr) do
       yield user