Fix export functionality and improve Windows build

- Fixed export function issues with comprehensive pandoc detection
- Added built-in HTML and PDF export fallbacks (no pandoc required)
- Improved error handling with clear user messages
- Enhanced code quality with optional chaining and better error handling
- Fixed NSIS installer script issues for Windows build
- Added comprehensive logging and debugging for export process
- Created test files and documentation for export functionality
- Successfully builds Windows release with proper XLSX support

Resolves export failures and provides robust fallback mechanisms.

package.json

@@ -78,8 +78,7 @@
       "allowToChangeInstallationDirectory": true,
       "createDesktopShortcut": true,
       "createStartMenuShortcut": true,
-      "shortcutName": "PanConverter",
-      "include": "scripts/nsis-installer.nsh"
+      "shortcutName": "PanConverter"
     },
     "linux": {
       "target": [