[M5] verify-curated-db.sh + boost recipe (header-only)

scripts/curated-snippets/protobuf.cpp

@@ -0,0 +1,8 @@
+#include <google/protobuf/arena.h>
+import std;
+
+int main() {
+    google::protobuf::Arena arena;
+    std::println("protobuf ok: arena size {}", arena.SpaceUsed());
+    return 0;
+}