fix(brush-core): exposed windows signal stubs as public re-export

pi-shell calls sys::signal::kill_process on the windows target; the
pub(crate) glob re-export made it invisible outside brush-core, unlike
the unix module where kill_process is pub. Mirrors unix visibility.

crates/vendor/brush-core/src/sys/windows.rs

@@ -11,7 +11,7 @@ pub use crate::sys::stubs::{poll, resource};
 pub mod signal {
 	pub(crate) use tokio::signal::ctrl_c as await_ctrl_c;
 
-	pub(crate) use crate::sys::stubs::signal::*;
+	pub use crate::sys::stubs::signal::*;
 }
 
 pub use crate::sys::tokio_process as process;