fix(receive): await Endpoint::close for iroh 0.97

[cbenhagen]

iroh 0.97 no longer closes connections gracefully when an Endpoint is dropped; you’re expected to await endpoint.close() before the last handle goes away (or you get the iroh::socket “dropped without close” error).

receive now clones the endpoint, runs the existing fetch/export logic in an inner async block, then close()s so that path runs on success and on ?/bail! errors. Ctrl+C closes the outer clone before exit. send is unchanged (Router::shutdown() already shuts the stack down).

Diff size: most of it is one extra indent level from wrapping the worker body; the behavioral change is small.

Test: CLI regression with RUST_LOG=iroh::socket=error and stderr checks, plus the usual byte equality check.