manifest: pin dockerImage to the deployed tag

The repo didn't record which image is live, so it couldn't answer "what is
deployed here?" — the tag lived only on the Cloudron app. Pin it to the image
deployed 2026-10-26 so the repo mirrors production, as our other repos do.

Consequence, same as librechat-custom: when the CLI runs from this directory this
manifest now wins over `cloudron update --image <tag>`, so a future release pins
the new tag here and commits it as part of the deploy.

CloudronManifest.json

@@ -26,5 +26,6 @@
   },
   "manifestVersion": 2,
   "website": "https://inference.coop",
-  "contactEmail": "info@inference.coop"
+  "contactEmail": "info@inference.coop",
-}
+  "dockerImage": "registry.inference.coop/co-op/member-portal:20261026-4920190"
+}