address pr comments

Author: SamSaffron

lib/utils/pdf_to_images.rb

@@ -73,7 +73,7 @@ def extract_pages
 
       @uploaded_pages = uploads
     ensure
-      FileUtils.rm_rf(temp_dir)
+      FileUtils.rm_rf(temp_dir) if temp_dir
     end
   end
 end

lib/utils/pdf_to_text.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class DiscourseAi::Utils::PdfToText
+  MAX_PDF_SIZE = 100.megabytes
+
   class Reader
     def initialize(upload:, user: nil, llm_model: nil)
       @extractor =