feat: add stakpak package (v0.3.86)

Stakpak is a DevOps AI agent that generates infrastructure code,
debugs Kubernetes, configures CI/CD, and automates deployments.

- Source: github.com/stakpak/agent v0.3.86
- Rust workspace (14 crates), default binary: stakpak
- Dependencies: openssl (transitive via native-tls), pkg-config
- License: Apache-2.0

packages/stakpak/default.nix

@@ -0,0 +1,5 @@
+{
+  pkgs,
+  ...
+}:
+pkgs.callPackage ./package.nix { }