update grid4 & heroledger models

heromodels/examples/grid4_example/README.md

@@ -0,0 +1,12 @@
+# Grid4 Node Example (OurDB)
+
+This example demonstrates how to use the Grid4 `Node` model against the embedded OurDB backend.
+
+- Creates an in-memory/on-disk OurDB under `/tmp`.
+- Demonstrates CRUD and simple index lookups on `country`, `nodegroupid`, and `pubkey`.
+
+Run it:
+
+```bash
+cargo run -p heromodels --example grid4_example
+```