feature(appimage): add appimage squashfs support for my nixos

hosts/argon/configuration.nix

@@ -2,6 +2,7 @@
 
 {
   imports = [
+    ../../modules/nixos/appimage.nix
     ../../modules/nixos/astro.nix
     ../../modules/nixos/audio.nix
     ../../modules/nixos/bootloader.nix

modules/nixos/appimage.nix

@@ -0,0 +1,19 @@
+{ config, lib, pkgs, ... }:
+
+{
+  # AppImages ship a squashfs payload that the bundled runtime mounts through
+  # libfuse.so.2 at startup. nix-ld resolves the ELF interpreter but not that
+  # dlopen, so running one directly dies with "dlopen(): error loading
+  # libfuse.so.2". appimage-run sidesteps the mount entirely: it unpacks the
+  # image and runs the payload inside an FHS sandbox, which the bundled Qt and
+  # electron style binaries need anyway.
+  #
+  # Used for the BitBox02 wallet AppImage, downloaded fresh from
+  # https://bitbox.swiss/download/ rather than installed from nixpkgs.
+  programs.appimage = {
+    enable = true;
+    # register AppImages with binfmt_misc so ./Something.AppImage runs as-is,
+    # no appimage-run prefix to remember.
+    binfmt = true;
+  };
+}