fix(peer): log disconnect cause; bind e2e browse listener on all interfaces

The brokered third-party browse e2e failed deterministically on CI. The test
bound its listener to 127.0.0.1 only, but the server brokers back the address
it observed for that client - the host's routable IP (172.17.0.2 under Docker,
10.x on a CI runner). The sharer's dial was refused, it fell back to
re-brokering, and the accept never arrived. The sibling third-party browse
tests already bind 0.0.0.0.

disconnect_with_error logged only "disconnect" and dropped the io::Error on the
floor, which is what made this invisible in the logs; it now logs the cause.

soulseek-rs-lib/src/actor/peer_actor.rs

@@ -609,7 +609,10 @@ impl PeerActor {
 
     fn disconnect_with_error(&mut self, error: Error) {
         let username = self.peer_username();
-        debug!("[peer:{}] disconnect", username);
+        // Include the cause: a failed outbound dial reports nothing else, so
+        // without it an unreachable peer is indistinguishable from a clean
+        // disconnect in the logs.
+        debug!("[peer:{}] disconnect: {}", username, error);
 
         self.stream.take();