The catalogue prepares its own schema instead of migrating at start

It brought its schema up inside its runtime, on every start. That made a schema it could not reach a
crash loop rather than a stop, with the module graph keeping a gap and nothing saying so — which is
how a whole morning's builds went unrecorded. The mesh now prepares this module's state before it
starts this version and does not start it if that failed (novox/hq ADR 0135): the work moves to an
entrypoint the image names in MESH_PREPARE, beside the entrypoints it already names.

The reason it was at start — that a step blocking the apply would block the very apply bringing the
overlay up — stopped being true when a step's failure became its module's business rather than the
machine's (ADR 0136).

modules/mesh-catalog/module.json

@@ -37,6 +37,7 @@
     "rebuild-needed",
     "catching-up"
   ],
+  "prepares": true,
   "resources": [
     {
       "id": "mesh-state",