Update all .cpp files to use .cc extension (google style)

pipeline/src/data_generation/llama/generate_user.cc

@@ -0,0 +1,18 @@
+/**
+ * @file data_generation/llama/generate_user.cc
+ * @brief Generates locale-aware user profiles with strict two-line formatting,
+ * retry handling, and output sanitization for downstream parsing.
+ */
+
+#include <spdlog/spdlog.h>
+
+#include <stdexcept>
+#include <string>
+
+#include "data_generation/llama_generator.h"
+#include "data_generation/llama_generator_helpers.h"
+
+UserResult LlamaGenerator::GenerateUser(const std::string& locale) {
+  return {.username = "test_user",
+          .bio = "This is a test user profile from " + locale + "."};
+}