feat(openclaw): add runtime closure meta-package for Harmonia caching

Creates openclaw-runtime-closure as a symlinkJoin of all runtime dependencies (nodejs_22, kubectl, jq, git, emacs, tsx, tea, python3.withPackages pymupdf, qmd) that will be pushed to the Harmonia binary cache by CI and pulled into the PVC by the init container at pod startup.

This meta-package enables the thin Docker image architecture where:
- The Docker image stays small (~1.5GB vs 2.7GB) with only /app, nix, and basics
- Runtime deps are fetched from Harmonia at pod startup via nix copy --from
- CI push is fast (thin image) and runtime deps are cached separately

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

flake.nix

@@ -308,6 +308,7 @@
               "nix-deck-kernel" = self.nixosConfigurations.nix-deck.config.boot.kernelPackages.kernel;
               # OpenClaw docker image (pulled + augmented with nix tools)
               "openclaw-image" = pkgs.custom.openclaw-image;
+              "openclaw-runtime-closure" = pkgs.custom.openclaw-runtime-closure;
             }
           else
             { }