CAT-BG2: mesh-build-go builds a Go package as its module zip and publishes it under its module path

Design 51 Publishing, ADR 0605 §3: a Go package is published from a trunk build through go-package-registry
under the version the builder gave it. The build packs the directory the artifact names as Go's module zip,
answers its digest and h1: sum, and on a version publishes it under the Go module path (the forge's Go seat
takes the name as the module path); a candidate publishes nothing. The ask's seat and version reach the build.

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

modules/mesh-build-go/module.json

@@ -74,7 +74,9 @@
   },
   "invokes": [
     "seat:oci-artifact-registry.publish",
-    "seat:oci-artifact-registry.publish-part"
+    "seat:oci-artifact-registry.publish-part",
+    "seat:go-package-registry.publish",
+    "seat:go-package-registry.publish-part"
   ],
   "own-secrets": {
     "broker": "${dir:state}/broker"