Refactor shell package and use getent for user/group lookup

client/internal/shell/getent_windows.go

@@ -0,0 +1,26 @@
+//go:build windows
+
+package shell
+
+import "os/user"
+
+// lookupWithGetent on Windows just delegates to os/user.Lookup.
+// Windows does not use NSS/getent; its user lookup works without CGO.
+func LookupWithGetent(username string) (*user.User, error) {
+	return user.Lookup(username)
+}
+
+// currentUserWithGetent on Windows just delegates to os/user.Current.
+func CurrentUserWithGetent() (*user.User, error) {
+	return user.Current()
+}
+
+// getShellFromGetent is a no-op on Windows; shell resolution uses PowerShell detection.
+func GetShellFromGetent(_ string) string {
+	return ""
+}
+
+// groupIdsWithFallback on Windows just delegates to u.GroupIds().
+func GroupIdsWithFallback(u *user.User) ([]string, error) {
+	return u.GroupIds()
+}