docs: add remaining docs for classes in app/logical.

app/logical/sqs_service.rb

@@ -1,14 +1,25 @@
+# A wrapper for the Amazon SQS API. Used by the PostArchive and PoolArchive
+# service to record post and pool versions.
+#
+# @see https://docs.aws.amazon.com/sqs/index.html
+# @see https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/SQS/Client.html
 class SqsService
   attr_reader :url
 
+  # @param url [String] the URL of the Amazon SQS queue
   def initialize(url)
     @url = url
   end
 
+  # @return [Boolean] true if the SQS service is configured
   def enabled?
     Danbooru.config.aws_credentials.set? && url.present?
   end
 
+  # Sends a message to the Amazon SQS queue.
+  # @param string [String] the message to send
+  # @param options [Hash] extra options for the SQS call
+  # @see https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/SQS/Client.html#send_message-instance_method
   def send_message(string, options = {})
     return unless enabled?
 
@@ -22,6 +33,7 @@ class SqsService
 
   private
 
+  # @return [Aws::SQS::Client] the SQS API client object
   def sqs
     @sqs ||= Aws::SQS::Client.new(
       credentials: Danbooru.config.aws_credentials,