feat: Add Settings UI, native OS Trash integration, and Floating Button

[GTRSM]

This PR transforms the extension from a simple script into a feature-rich tool, while maintaining strict backward compatibility.

Key Features:

1. Settings Dialog: Added a GUI (via vlc.dialog) to configure extension preferences.
2. Native Trash / Recycle Bin Integration: Safely moves files to the OS Trash instead of permanent destruction. Supports gio trash / trash-put (Linux), osascript (macOS), and PowerShell (Windows).
3. Floating 'Always On Top' Button: Added a persistent UI button that allows 1-click deletion while watching a video without navigating menus.
4. Configuration Persistence: Saves user settings to ~/.vlc-delete-config.json or %APPDATA%\vlc\vlc-delete-config.json.
5. Robust Cross-Platform Fixes: Added proper POSIX shell escaping to prevent command injection risks, implemented safe fallbacks for missing environment variables, and dramatically reduced CPU spin-loop blocking in sleep().
6. XFCE/Qt Menu Workaround: Implemented a fallback where clicking 'VLC Delete' while no video is playing automatically opens the Settings window. This elegantly bypasses a known issue on some Linux desktop environments where Qt fails to render extension sub-menus automatically.

I have extensively tested these changes. Please let me know if you have any questions!

[GTRSM]

I should add that my testing was on my Linux machine, running Xubuntu 22.04.

I don't have a OSX, or Windows machine to test, so your mileage may vary.