Adhere to the icon theme of the host DE/OS.

[RokeJulianLockhart]

1. Is your feature request related to a problem? Please describe.

   Solely NAPS2's icons differ from those of the rest of my OS's:

   1. 

      https://github.com/cyanfish/naps2/releases/download/v7.4.0/naps2-7.4.0-linux-x64.rpm

      versus

   2. 

      https://download.opensuse.org/repositories/openSUSE:/Factory/standard/x86_64/kf6-breeze-icons-6.0.0-1.1.x86_64.rpm

2. Describe the solution you'd like

   Adhere to https://specifications.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html#definitions.

3. Describe alternatives you've considered

   A kind of reimplementation of what https://www.reddit.com/r/flatpak/comments/irhzb0/comment/g4yonp6/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button describes, but that would be irrational.

4. Additional context

   I've tested https://github.com/cyanfish/naps2/releases/download/v7.4.0/naps2-7.4.0-linux-x64.flatpak and https://github.com/cyanfish/naps2/releases/download/v7.4.0/naps2-7.4.0-linux-x64.rpm on cpe:/o:kde:plasma:6.0.2 on cpe:/o:opensuse:tumbleweed:20240320.

[cyanfish]

I am open to the possibility of adding a "Theme" setting, and there could be something like a "Freedesktop" option on Linux.

This isn't something I'm likely to prioritize any time soon, but if someone else wants to make a PR for this I'd be happy to give some pointers.