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

scripts/curated-snippets/nlohmann_json.cpp

@@ -0,0 +1,9 @@
+#include <nlohmann/json.hpp>
+import std;
+
+int main() {
+    nlohmann::json j;
+    j["k"] = 42;
+    std::println("{}", j.dump());
+    return 0;
+}