No campus's address ships in the repo

prodcom-transcript's endpoint defaulted to 10.3.11.152:24480 — Apollo
Beach's ProdCom. A fresh install anywhere therefore came up reading AB's
comms and reported itself healthy doing it: that is exactly what the new
North Attleboro install did. The default is now blank, so a new install
says "No ProdCom server configured" (in red, as the ProPresenter modules
already do for a missing host) until someone points it at the ProdCom for
that location. Setting a host still connects as before.

The same address is out of SPEC.md's worked example, CLAUDE.md's note
about the reference app, and the prodcom-listener snapshot's config,
README and fallback — that fallback now exits with a line telling the
operator what to set, rather than throwing on an empty URL.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

SPEC.md

@@ -129,7 +129,7 @@ modules/<id>/
   "minSize": { "w": 2, "h": 2 },
   "defaultSize": { "w": 4, "h": 3 },
   "configSchema": {
-    "prodcomUrl": { "type": "string", "label": "ProdCom URL", "default": "http://10.3.11.152:24480" },
+    "prodcomUrl": { "type": "string", "label": "ProdCom URL", "default": "" },
     "apiKey":     { "type": "password", "label": "API key (if PSK auth enabled)", "default": "" }
   },
   "instanceSchema": {