distribution provides artifact-store again beside its new roles, for the running node-engines (issue 1966)

The registry milestone renamed what distribution offers (container-image-registry, oci-artifact-registry,
mesh-artifact-store), as ADR 0632 section 3 decides. The node-engines running on every node are the ones
from before it: they find the store through the provision artifact-store, so they fetch no new build,
including their own successor, and keep running what they ran. ADR 0632 section 2's guarantee (no node loses
the store while its engine reads it the old way) lives in the new indexer's hold, which the running indexer
predates. So this goes against ADR 0632 section 3 for a limited time, at the operator's word (bootstrap of
2026-11-07, no new record): offered again beside the new roles until every node-engine runs the registry
milestone's build, then removed in the next change to distribution.

Claude-Session: https://claude.ai/code/session_01NcbgfFSnn24M3GcqttoU7i

modules/distribution/module.json

@@ -4,6 +4,20 @@
   "packages": {
     "builds": "0.1"
   },
+  "provides": [
+    {
+      "name": "artifact-store",
+      "scope": "mesh",
+      "credential": {
+        "form": "none"
+      }
+    }
+  ],
+  "serves": {
+    "artifact-store": {
+      "port": 5000
+    }
+  },
   "claims": [
     {
       "name": "container-image-registry",