docs,examples: graceful shutdown — new examples/graceful_shutdown.rs, README 'Stopping actors', named_genserver uses shutdown(), Deep Dive terminate note, ROADMAP open items

examples/named_genserver.rs

@@ -66,6 +66,12 @@ fn main() {
         let svc: Option<GenServerRef<Counter>> = whereis_server(COUNTER);
         if let Some(svc) = svc {
             let _ = svc.call(Query::Get);
+            // A named server is pinned alive by the registry, so dropping refs
+            // does not end it. Stop it explicitly: `shutdown()` asks politely
+            // (a trapping server drains first; this one is stopped outright)
+            // and waits until it is gone. Left running, the root's return
+            // would shut it down the same way — see examples/graceful_shutdown.rs.
+            svc.shutdown();
         }
     });
 }