Decouple marble-kit from PNPM dependencies list to simplify flake.nix.

[Ezjfc]

Background

Previously, the sponsor-only dependency marble-kit must be fetched with an extended PNPM fetcher:

marble-shell/flake.nix

Lines 47 to 53 in 216a40a

	sshKey = inputs.sshKey;
	prePnpmInstall = ''
	export PATH="$PATH:${pkgs.git}/bin":${pkgs.openssh}/bin
	eval "$(ssh-agent -s)"
	ssh-add $sshKey
	export GIT_SSH_COMMAND="ssh -o StrictHostKeyChecking=no"
	'';

Not only is this cumbersome, defeating the point of the identical inputs.marble, but it also requires adding the SSH key to/nix/store, which is substantially insecure, as stated in README.md of agenix.

This pull request makes a copy of the dependencies list (nix/package.json and nix/pnpm-lock.yaml) and sets marble to point to /nix/kit, which is populated with inputs.marble during build time.

Extra

The PNPM fetcher (version 2) is also outdated and has been removed from 26.11. Attempts to change the fetcher version were tested to be unsuccessful, such as

marble.overrideAttrs (prev: {
  pnpmDeps = prev.pnpmDeps.overrideAttrs {
    fetcherVersion = 3;
  }
})

which will always result in

error: fetchPnpmDeps: `fetcherVersion = 2` was removed in the 26.11 release. Please migrate `marble` to `fetcherVersion = 3` and regenerate the hash. See https://nixos.org/manual/nixpkgs/stable/#javascript-pnpm-fetcherVersion.

Therefore, this pull request also updates inputs.nixpkgs alongside the code of the fetcher.

Moreover, pkgs.pnpm.configHook is deprecated in favour of pkgs.pnpmConfigHook:

evaluation warning: pnpm.configHook: The package attribute is deprecated. Use the top-level pnpmConfigHook attribute instead

Lastly, inputs.sshKey is removed as it is no longer used by the flake.

[Ezjfc]

Note that this section will become obsolete but I am unsure of the appropriate changes for it:

marble-shell/README.md

Lines 106 to 124 in 216a40a

	2. Override the package and include your ssh key.
	```nix
	inputs: let
	{ pkgs, inputs, ... }: let
	marble = inputs.marble-shell.packages.${pkgs.system}.default;
	marble-shell = marble.overrideAttrs (prev: {
	pnpmDeps = prev.pnpmDeps.overrideAttrs {
	sshKey = ./path/to/sshkey;
	};
	});
	in {
	# using home-manager
	home.packages = [marble-shell];
	# using configuration.nix
	environment.systemPackages = [marble-shell];
	}
	```

[Ezjfc]

Unfortunately, updating nixpkgs to the latest results in this error:

(gjs:48988): Gjs-CRITICAL **: 02:23:00.211: JS ERROR: Error: Requiring GlyGtk4, version none: Typelib file for namespace 'GlyGtk4' (any version) not found
require@resource:///org/gnome/gjs/modules/esm/gi.js:16:28
@gi://GlyGtk4:3:25

(gjs:48988): Gjs-CRITICAL **: 02:23:00.211: Module file:///run/user/1000/ags.js threw an exception
error: exit status 1

Currently, I have no clue what went wrong.

[Ezjfc]

This fix in the Marble Kit should resovle the above error: https://github.com/marble-shell/kit/issues/6