fix: keep OpenRPC ServerHandle alive to prevent server shutdown

The ServerHandle was being dropped immediately after spawning, causing the
OpenRPC server to shut down. Now we properly await handle.stopped() to keep
the server running.

examples/osiris_openrpc/README.md

@@ -18,6 +18,14 @@ This example demonstrates the complete workflow of using Hero Supervisor with OS
 
 ## Prerequisites
 
+**IMPORTANT: Redis must be running before starting this example!**
+
+```bash
+# Start Redis (if not already running)
+redis-server
+```
+
+Other requirements:
 - Redis server running on `localhost:6379`
 - Rust toolchain installed
 - Both `supervisor` and `runner_rust` crates available