feat(nix): generate module options docs and sync to website

- Add nix/generate-hm-options.nix to export HM and NixOS module options as JSON via nixosOptionsDoc
- Expose hm-options-json and nixos-options-json packages in flake.nix
- Add CI workflow to auto-build and push JSONs to mangowm.github.io on module changes
- Add missing description to hm-modules enable option

nix/hm-modules.nix

@@ -22,6 +22,7 @@ in
       enable = mkOption {
         type = types.bool;
         default = false;
+        description = "Whether to enable mangowm, a Wayland compositor based on dwl.";
       };
       package = lib.mkOption {
         type = lib.types.package;