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

scripts/curated-snippets/eigen.cpp

@@ -0,0 +1,8 @@
+#include <Eigen/Core>
+import std;
+
+int main() {
+    Eigen::Vector2d v(1.0, 2.0);
+    std::println("eigen ok: ({},{})", v[0], v[1]);
+    return 0;
+}