feat: redesign the project structure

modules/nixos/fhs-fonts.nix

@@ -0,0 +1,26 @@
+# copy from https://github.com/NixOS/nixpkgs/issues/119433#issuecomment-1326957279
+# mainly for flatpak
+# bindfs resolves all symlink, 
+# allowing all fonts to be accessed at `/usr/share/fonts`
+# without letting /nix into the sandbox.
+{ config, pkgs, ... }:
+
+{
+  system.fsPackages = [ pkgs.bindfs ];
+  fileSystems = let
+    mkRoSymBind = path: {
+      device = path;
+      fsType = "fuse.bindfs";
+      options = [ "ro" "resolve-symlinks" "x-gvfs-hide" ];
+    };
+    aggregatedFonts = pkgs.buildEnv {
+      name = "system-fonts";
+      paths = config.fonts.fonts;
+      pathsToLink = [ "/share/fonts" ];
+    };
+  in {
+    # Create an FHS mount to support flatpak host icons/fonts
+    "/usr/share/icons" = mkRoSymBind (config.system.path + "/share/icons");
+    "/usr/share/fonts" = mkRoSymBind (aggregatedFonts + "/share/fonts");
+  };
+}