[Packaging] Fix Linux RPM icon/cache refresh after upgrades

[shadowbipnode]

Linux RPM upgrades may keep stale desktop icons or cached application metadata, especially on Rocky Linux/GNOME.

Current behavior:

• old icon may persist after update
• desktop entry/icon cache may not refresh correctly
• users may need manual remove/reinstall

Goals:

• deterministic icon refresh after RPM upgrade
• proper desktop database/icon cache invalidation
• improved RPM postinstall/postun behavior
• verify Rocky/GNOME/KDE upgrade behavior
• avoid stale app metadata after upgrades