feat: improve nix-update workflow and update packages

- Refactor nix-update.yml: push directly to master instead of PRs
- Add skip list for packages without upstream releases
- Add opencode subpackage handling for node_modules
- Add nix-update-script to beads, code2prompt, mem0
- Update mem0: 1.0.0 -> 1.0.2
- Update opencode: 1.1.18 -> 1.1.25
- Fix n8n tag format
- Add n8n update.sh helper script

pkgs/code2prompt/default.nix

@@ -1,6 +1,7 @@
 {
   lib,
   fetchFromGitHub,
+  nix-update-script,
   rustPlatform,
   pkg-config,
   perl,
@@ -27,6 +28,8 @@ rustPlatform.buildRustPackage rec {
 
   buildInputs = [openssl];
 
+  passthru.updateScript = nix-update-script {};
+
   meta = with lib; {
     description = "A CLI tool that converts your codebase into a single LLM prompt with a source tree, prompt templating, and token counting";
     homepage = "https://github.com/mufeedvh/code2prompt";