FIX: avoid using structured outputs for report runs (#1502)

Structured outputs are prone to formatting issue, especially around newlines
and custom pieces of text that need escaping.

This avoids using it for the automation reporting.

Particularly previous to this fix o4-mini based reports were broken

lib/automation/report_runner.rb

@@ -154,12 +154,10 @@ module DiscourseAi
         result = +""
         bot = DiscourseAi::Personas::Bot.as(Discourse.system_user, persona: @persona, model: @model)
         json_summary_schema_key = @persona.response_format&.first.to_h
-        output = nil
 
         buffer_blk =
           Proc.new do |partial, _, type|
             if type == :structured_output
-              output = partial.dup
               read_chunk = partial.read_buffered_property(json_summary_schema_key["key"]&.to_sym)
 
               print read_chunk if Rails.env.development? && @debug_mode

lib/personas/report_runner.rb

@@ -17,18 +17,9 @@ module DiscourseAi
 
           Follow the provided writing composition instructions carefully and precisely step-by-step.
 
-          Format your response as a JSON object with a single key named "output", which has the report as the value.
-          Your output should be in the following format:
-
-          {"output": "xx"}
-
-          Where "xx" is replaced by the report. Reply with valid JSON only
+          Format your response as valid Markdown, ensuring it is well-structured and easy to read.
         PROMPT
       end
-
-      def response_format
-        [{ "key" => "output", "type" => "string" }]
-      end
     end
   end
 end