fix: Disable code signing to avoid Windows symlink errors

- Add signAndEditExecutable: false to skip code signing on Windows
- Clear electron-builder winCodeSign cache before build
- Add helpful error messages for symlink permission issues

The winCodeSign package contains macOS symlinks that fail to extract
on Windows without admin privileges or Developer Mode enabled.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/build-client.bat

@@ -206,6 +206,14 @@ echo %BLUE%[STEP]%NC% 打包 Electron 應用...
 cd /d "%CLIENT_DIR%"
 
 echo %BLUE%[INFO]%NC% 目標平台: Windows (Portable)
+
+REM 清理可能損壞的 electron-builder 快取（解決 symlink 問題）
+set "EB_CACHE=%LOCALAPPDATA%\electron-builder\Cache\winCodeSign"
+if exist "%EB_CACHE%" (
+    echo %BLUE%[INFO]%NC% 清理 electron-builder 快取...
+    rmdir /s /q "%EB_CACHE%" 2>nul
+)
+
 echo %BLUE%[INFO]%NC% 執行 electron-builder...
 
 REM 使用 npm run build 或直接執行 node_modules 中的 electron-builder
@@ -217,6 +225,9 @@ if exist "node_modules\.bin\electron-builder.cmd" (
 
 if errorlevel 1 (
     echo %RED%[ERROR]%NC% electron-builder 執行失敗
+    echo %YELLOW%[WARN]%NC% 如果出現 symlink 錯誤，請嘗試以下方案：
+    echo %YELLOW%[WARN]%NC%   1. 以系統管理員身分執行此腳本
+    echo %YELLOW%[WARN]%NC%   2. 或啟用 Windows 開發人員模式（設定 ^> 更新與安全性 ^> 開發人員專用）
     exit /b 1
 )