brokerd: escape container errors in the log; prefix and quote two messages

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/brokerd/src/main.rs

@@ -97,7 +97,7 @@ fn main() -> ExitCode {
         broker_path.display(),
         admin_path.display()
     );
-    eprintln!("{runtime_notice}");
+    eprintln!("brokerd: {runtime_notice}");
 
     match started.run() {
         Ok(()) => ExitCode::SUCCESS,