Add ability to set current image as desktop wallpaper with keyboard
shortcut 'W' and icon button in Properties panel.
Supports COSMIC, GNOME, KDE, XFCE, and tiling window managers via
automatic detection and fallback mechanism.
Implementation uses wallpaper crate with custom COSMIC config file
integration and gsettings/feh fallbacks.
- Add explicit lifetimes to Element return types
- Remove unused imports (Length, button, horizontal_space, icon, Handle, self)
- Mark unused parameter with underscore prefix
This eliminates all 'hiding a lifetime' and 'unused import' warnings.
Replace hardcoded \"~/Pictures\" with dirs::picture_dir() which resolves
to the actual absolute path (e.g. /home/user/Pictures).
The tilde (~) in paths is not automatically expanded by Rust's PathBuf,
causing path.exists() to return false for \"~/Pictures\".
Using dirs::picture_dir() provides:
- Proper absolute path resolution
- XDG Base Directory compliance
- Fallback to home directory if Pictures doesn't exist
Note: Users with existing config files need to delete
~/.config/cosmic/org.codeberg.wfx.Noctua/v1/default_image_dir
to apply the new default."
