Add portable mode support for Persepolis

[mgh12453]

Summary

This PR adds portable mode support to Persepolis, allowing the application to store all configuration, settings, and download data in a directory alongside the executable rather than in the user's home directory. This is useful for running Persepolis from USB drives or other portable storage.

Key Changes

• Portable mode detection: Added _getPortableMarkerDir(), isPortableMode(), and setForcePortableMode() functions to detect and manage portable mode via a portable marker file or --portable CLI argument
• Centralized QSettings creation: Introduced createQSettings() function that returns platform-appropriate QSettings (INI file in portable mode, registry/defaults in normal mode)
• Config folder redirection: Modified determineConfigFolder() to return persepolis_data subdirectory when in portable mode
• Download path adjustment: Updated returnDefaultSettings() to use portable data directory for downloads in portable mode
• CLI argument support: Added --portable command-line flag that forces portable mode and creates the marker file if needed
• Windows mutex isolation: Modified Windows mutex naming to include a hash of the config path in portable mode, allowing multiple portable instances to run simultaneously
• Browser integration disable: Disabled browser native messaging integration in portable mode to avoid system-wide registry/config modifications
• Early initialization: Added early portable mode detection in persepolis.py before any config folders are computed
• Consistent QSettings usage: Updated all QSettings instantiations across the codebase to use createQSettings() for consistency
• Browser integration script support: Added portable mode detection to PersepolisBI.py for the browser integration helper

Implementation Details

• The portable marker file is created automatically when --portable is used if it doesn't already exist
• Portable mode works with both bundled (PyInstaller/Nuitka) and source installations
• The portable.example file serves as documentation for manual portable mode activation
• All data paths (settings, database, downloads) are redirected to the persepolis_data subdirectory in portable mode
• The implementation maintains backward compatibility with existing non-portable installations