Updated GTK3 icon rendering paths in affected UI helpers to call gtkutil_image_new_from_stock(...), which is the path that resolves zc-menu-* resources correctly and consistently from data/icons/menu (instead of raw theme lookup).
Added new icons to the shared bundled menu icon set (light/dark) for copy, delete, add, remove, spell-check, and refresh, and registered them in the GResource manifest so they are always available at runtime.
Added the new network-list SVG icon in both light and dark variants under data/icons/menu, so it comes from the same icon set as the rest of the menu icons.
Registered both new icon files in the compiled GResource manifest so they are available through the existing resource-loading path.
