postgres: its server container is not named after the seat

The module's server container was called mesh-store and its data directory
/var/lib/mesh-store — the seat's name reused for the module's own resources,
a leftover from the first migration. On a machine whose postgres holds no
seat (ace, as a database provider only) that produced a container called
mesh-store holding nothing of the kind. The container is now named
postgres. The data directory keeps its path: a path change recreates a
running container on an empty directory (hq 126), and novox's store lives
there.

Rolling this out recreates novox's store container once (a restart on its
bind mount, no data moves). The two catalogue-test failures on this branch
(resolver_manifests_test) fail identically on main today.

modules/postgres/module.json

@@ -80,7 +80,7 @@
     {
       "id": "server",
       "type": "container",
-      "name": "mesh-store",
+      "name": "postgres",
       "image": "pgvector/pgvector@sha256:cf134a767f474095eeba57e0117be8e568e011a63f33fbf252f14c9b760f8e6f",
       "env": {
         "POSTGRES_PASSWORD_FILE": "/run/secrets/superuser",