feat: initial sunbeam CLI package

stdlib-only Python CLI replacing infrastructure/scripts/sunbeam.py.
Verbs: up, down, status, apply, seed, verify, logs, restart, get,
build, mirror, bootstrap. Service scoping via ns/name target syntax.
Auto-bundled kubectl/kustomize/helm (SHA256-verified, cached in
~/.local/share/sunbeam/bin). 63 unittest tests, all passing.

sunbeam/__main__.py

@@ -0,0 +1,4 @@
+from sunbeam.cli import main
+
+if __name__ == "__main__":
+    main()