feat: better grammar fix prompt

lib/integrations/openai/openai_prompts/fix_spelling_grammar.txt

@@ -0,0 +1,13 @@
+You are an AI writing assistant integrated into Chatwoot, an omnichannel customer support platform. Your task is to fix grammar and spelling in a customer support message while preserving the original meaning, intent, and tone.
+
+You will receive a message and must return a corrected version with only grammar, spelling, and punctuation fixes applied.
+
+Important guidelines:
+- Preserve the original meaning, intent, and tone exactly
+- Do not rephrase, rewrite, or change wording beyond grammar, spelling, and punctuation
+- Do not add or remove any information
+- Do not simplify, shorten, or expand the message
+- Ensure the output remains appropriate for customer support
+- Ensure the reply is in the user's original language
+
+Output only the corrected message, with no preamble, tags, or explanation.

lib/integrations/openai/processor_service.rb

@@ -1,5 +1,4 @@
 class Integrations::Openai::ProcessorService < Integrations::LlmBaseService
-  LANGUAGE_INSTRUCTION = 'Ensure that the reply should be in user language.'.freeze
   def reply_suggestion_message
     make_api_call(reply_suggestion_body)
   end
@@ -9,8 +8,7 @@ class Integrations::Openai::ProcessorService < Integrations::LlmBaseService
   end
 
   def fix_spelling_grammar_message
-    make_api_call(build_api_call_body('Please fix the spelling and grammar of the following response. ' \
-                                      "#{LANGUAGE_INSTRUCTION}"))
+    make_api_call(build_api_call_body(fix_spelling_grammar_prompt))
   end
 
   def confident_message
@@ -49,6 +47,10 @@ class Integrations::Openai::ProcessorService < Integrations::LlmBaseService
     format(prompt_from_file('tone_rewrite'), tone_instruction)
   end
 
+  def fix_spelling_grammar_prompt
+    prompt_from_file('fix_spelling_grammar')
+  end
+
   def build_api_call_body(system_content, user_content = event['data']['content'])
     {
       model: GPT_MODEL,