Add Windows Explorer context menu integration

- Add context menu entries for all supported file types
- Implement CLI interface with --convert and --convert-to commands
- Create installation/uninstallation scripts (registry, PowerShell, batch)
- Add NSIS installer integration for automatic context menu setup
- Support direct conversion from right-click menu
- Include comprehensive documentation and usage instructions

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

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

scripts/install-context-menu.bat

@@ -0,0 +1,48 @@
+@echo off
+echo PanConverter Context Menu Installation
+echo =====================================
+echo.
+
+REM Check for administrator privileges
+net session >nul 2>&1
+if %errorLevel% == 0 (
+    echo Running with administrator privileges...
+) else (
+    echo This script requires administrator privileges.
+    echo Please right-click and select "Run as administrator"
+    echo.
+    pause
+    exit /b 1
+)
+
+REM Check if PanConverter is installed
+if not exist "%LOCALAPPDATA%\Programs\PanConverter\PanConverter.exe" (
+    echo Warning: PanConverter not found at the expected location.
+    echo Please ensure PanConverter is installed before continuing.
+    echo Expected location: %LOCALAPPDATA%\Programs\PanConverter\PanConverter.exe
+    echo.
+    set /p continue="Continue anyway? (y/N): "
+    if /i not "%continue%"=="y" exit /b 1
+)
+
+echo Installing context menu entries...
+reg import "%~dp0install-context-menu.reg"
+
+if %errorLevel% == 0 (
+    echo.
+    echo Context menu integration installed successfully!
+    echo.
+    echo You can now right-click on supported files and select:
+    echo • "Convert with PanConverter" - Shows conversion dialog  
+    echo • "PanConverter > Convert to..." - Direct conversion ^(for Markdown^)
+    echo.
+    echo Supported file types:
+    echo .md .markdown .html .htm .docx .odt .rtf .tex .pdf .pptx .ppt .odp
+) else (
+    echo.
+    echo Failed to install context menu entries.
+    echo Please check that the registry file exists and try again.
+)
+
+echo.
+pause