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/uninstall-context-menu.bat

@@ -0,0 +1,32 @@
+@echo off
+echo PanConverter Context Menu Uninstallation
+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
+)
+
+echo Removing context menu entries...
+reg import "%~dp0uninstall-context-menu.reg"
+
+if %errorLevel% == 0 (
+    echo.
+    echo Context menu integration removed successfully!
+    echo PanConverter entries have been removed from the Windows Explorer context menu.
+) else (
+    echo.
+    echo Failed to remove context menu entries.
+    echo Please check that the registry file exists and try again.
+)
+
+echo.
+pause