docs(web): clarify that --bind takes a host or IP, not an interface name

The flag's value is concatenated with ":PORT" and passed to
http.ListenAndServe, so it has always been a host/IP. The previous help
text invited users to pass an interface name like "eth0", which then
failed with a confusing DNS lookup error.

Refs #264.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cmd/soundtouch-web/main.go

@@ -36,7 +36,7 @@ func main() {
 			},
 			&cli.StringFlag{
 				Name:    "bind",
-				Usage:   "Network interface to bind to",
+				Usage:   "Address (host or IP) for the HTTP listener; leave empty to listen on all interfaces",
 				EnvVars: []string{"BIND_ADDR"},
 			},
 		},