fix: kill and wait stremio-runtime child after readers finish

After both stdout and stderr readers exited, the Child handle was just
dropped at the end of the match arm. On Windows std::process::Child's
Drop neither kills nor waits, so the OS process kept its kernel object
(and its bound ports) alive until either the JobObject KILL_ON_JOB_CLOSE
fired on shell exit or init adopted it.

In the crash-restart path this is worse: a fresh start() is launched
while the previous runtime is still being reaped, and both processes
race for port 11470.

Explicitly kill().ok() + wait().ok() once the readers see EOF so the
previous runtime is gone before we report 'Server terminated.' and fire
the crash notice. Errors from killing an already-exited child are
intentionally swallowed.

Closes #50

src/stremio_app/stremio_server/server.rs

@@ -178,6 +178,9 @@ impl StremioServer {
                     });
                     out_thread.join().ok();
                     err_thread.join().ok();
+                    // Drop on Windows neither kills nor waits, so reap explicitly.
+                    child.kill().ok();
+                    child.wait().ok();
                 }
                 Err(err) => {
                     nwg::error_message(