Add Windows installer packaging (Setup.exe + portable exe)

PyInstaller onedir/onefile specs, Inno Setup script, and GitHub Actions
workflow to produce JUC500-Setup-win64.exe and portable builds.

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

juc500_app.py

@@ -0,0 +1,23 @@
+"""PyInstaller / Windows 엔트리 — 인자 없으면 GUI, 있으면 CLI."""
+
+from __future__ import annotations
+
+import sys
+
+
+def main() -> int:
+    argv = sys.argv[1:]
+    # 더블클릭 / 바로가기: GUI
+    if not argv:
+        from juc500_xfer.gui_server import run_gui
+
+        run_gui(open_browser=True)
+        return 0
+    # 하위 호환: 첫 인자가 옵션이 아니면 CLI
+    from juc500_xfer.cli import main as cli_main
+
+    return cli_main(argv)
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())