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/beads/default.nix

@@ -5,6 +5,7 @@
   fetchFromGitHub,
   gitMinimal,
   installShellFiles,
+  nix-update-script,
   versionCheckHook,
   writableTmpDirAsHomeHook,
 }:
@@ -49,9 +50,10 @@ buildGoModule (finalAttrs: {
   versionCheckProgramArg = "version";
   doInstallCheck = true;
 
-  # Tests require git worktree operations that fail in Nix sandbox
   doCheck = false;
 
+  passthru.updateScript = nix-update-script {};
+
   meta = {
     description = "Lightweight memory system for AI coding agents with graph-based issue tracking";
     homepage = "https://github.com/steveyegge/beads";