Add Copy to Menu Feature
This commit introduces a new "Copy" functionality to the application menu, allowing users to easily copy diagram content to the clipboard in various formats. The implementation includes:

New Features:

• Added "Copy" submenu to the File menu with multiple export options
• Implemented clipboard copy functionality for:
  • PNG image with transparent background
  • Generic SQL script
  • PostgreSQL script
  • JSON diagram representation

Technical Changes:

• Enhanced useExportDiagram hook with copyImageToClipboard function
• Updated export image context to support clipboard operations
• Added new localization strings for copy functionality across all supported languages (24 locale files updated)
• Implemented clipboard API integration for image and text content

UI Improvements:

• Integrated new menu items with appropriate icons and keyboard shortcuts
• Added proper error handling for clipboard operations
• This feature improves user experience by providing quick access to diagram exports without requiring file downloads.