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/n8n/default.nix

@@ -23,7 +23,7 @@ stdenv.mkDerivation (finalAttrs: {
   src = fetchFromGitHub {
     owner = "n8n-io";
     repo = "n8n";
-    tag = "n8n@${finalAttrs.version}";
+    tag = finalAttrs.version;
     hash = "sha256-EQP9ZI8kt30SUYE1+/UUpxQXpavzKqDu8qE24zsNifg=";
   };