fix: harden Unix scripts and Makefile

scripts/sync-items.sh

@@ -6,12 +6,12 @@ set -euo pipefail
 DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 
 PY=""
-if command -v python3 >/dev/null 2>&1; then
+if command -v python3 >/dev/null 2>&1 && python3 -c "import sys" >/dev/null 2>&1; then
   PY="python3"
-elif command -v python >/dev/null 2>&1; then
+elif command -v python >/dev/null 2>&1 && python -c "import sys" >/dev/null 2>&1; then
   PY="python"
 else
-  echo "[错误] 未找到 python3 / python, 请先安装 Python 3。" >&2
+  echo "[错误] 未找到可用的 python3 / python, 请先安装 Python 3。" >&2
   exit 1
 fi