Serve a seat's verbs from the membership once one is issued (novox/hq issue 218)

The runtime added every seat its start-up credential claims even after the mesh issued a
membership without it. A seat held once for the mesh is claimed on every machine running the
module, so ace's postgres announced the store seat the bus then refused it on.

node-tools/test/fixtures/store-claimant.mjs

@@ -0,0 +1,13 @@
+// A copy for the issue 218 test: a fixture registers once per process, at import.
+// A module that is both software and a role: postgres's own tools under its name, and its
+// implementation of the mesh-store seat's verbs under the seat's (novox/hq ADR 0159, 0160).
+import { registerModuleTools } from "@novox/mesh-sdk/tools";
+
+registerModuleTools("postgres", () => [
+  { name: "postgres_create_database", description: "make one", input: {}, run: async () => ({ made: true }) },
+  { name: "databases", description: "postgres's own listing", input: {}, run: async () => ({ software: "postgres" }) },
+]);
+
+registerModuleTools("mesh-store", () => [
+  { name: "databases", description: "what the store holds", input: {}, run: async () => ({ seat: "mesh-store" }) },
+]);