fix: stabilize Gemma 4 brewery generation

remove misleading turn-token output guidance from the brewery prompt
extract the last balanced JSON object before validation
keep README model setup and run instructions aligned
preserve Gemma 4 sampling defaults and local model usage

pipeline/includes/data_generation/llama_generator_helpers.h

@@ -77,4 +77,12 @@ std::string ValidateBreweryJsonPublic(const std::string& raw,
                                       std::string& name_out,
                                       std::string& description_out);
 
+/**
+ * @brief Extracts the last balanced JSON object from text.
+ *
+ * @param text Input text.
+ * @return Extracted JSON object or an empty string if none exists.
+ */
+std::string ExtractLastJsonObjectPublic(const std::string& text);
+
 #endif  // BIERGARTEN_PIPELINE_DATA_GENERATION_LLAMA_GENERATOR_HELPERS_H_