Fix missing _is_not_supported and harden WinUSB config cache

Restores the helper accidentally removed when adding access-denied
handling, retries I/O after seeding pyusb config index on Windows, and
handles USB overflow reads without crashing the HELLO loop.

Co-authored-by: Cursor <cursoragent@cursor.com>

start.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+# JUC500 GUI 실행 (인자 없으면 GUI, 있으면 CLI로 전달)
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")" && pwd)"
+cd "$ROOT"
+
+if [[ -x "$ROOT/.venv/bin/python" ]]; then
+  PY="$ROOT/.venv/bin/python"
+elif command -v python3 >/dev/null 2>&1; then
+  PY="$(command -v python3)"
+else
+  echo "Python3 가 없습니다. 먼저 설치하세요:" >&2
+  echo "  ./scripts/setup_macos.sh" >&2
+  exit 1
+fi
+
+if [[ ! -x "$ROOT/.venv/bin/python" ]]; then
+  echo "경고: .venv 없음 — 시스템 Python 사용. 문제가 있으면 ./scripts/setup_macos.sh" >&2
+fi
+
+export PYTHONPATH="$ROOT${PYTHONPATH:+:$PYTHONPATH}"
+
+# 의존성 빠른 확인
+if ! "$PY" -c "import usb" 2>/dev/null; then
+  echo "pyusb 가 없습니다. 먼저 설치하세요:" >&2
+  echo "  ./scripts/setup_macos.sh" >&2
+  exit 1
+fi
+
+exec "$PY" "$ROOT/juc500_app.py" "$@"