refactor: add PATH search logic to cargo-xwin wrapper script to find real binary outside script directory

Replace direct cargo xwin execution with PATH traversal to locate actual cargo-xwin binary outside script's own directory. Add error handling with installation instructions when binary not found. Skip script's own directory and empty PATH entries during search.

desktop-client/scripts/cargo-xwin

@@ -9,4 +9,27 @@ if ! command -v clang-cl >/dev/null 2>&1; then
   exit 1
 fi
 
-exec cargo xwin "$@"
+SELF_DIR="$(cd "$(dirname "$0")" && pwd)"
+REAL_CARGO_XWIN=""
+
+IFS=':'
+for dir in ${PATH}; do
+  if [ -z "${dir}" ] || [ "${dir}" = "${SELF_DIR}" ]; then
+    continue
+  fi
+
+  if [ -x "${dir}/cargo-xwin" ]; then
+    REAL_CARGO_XWIN="${dir}/cargo-xwin"
+    break
+  fi
+done
+unset IFS
+
+if [ -z "${REAL_CARGO_XWIN}" ]; then
+  echo "cargo-xwin binary was not found outside ${SELF_DIR}."
+  echo "Install it with:"
+  echo "  cargo install --locked cargo-xwin"
+  exit 1
+fi
+
+exec "${REAL_CARGO_XWIN}" "$@"