Apply App Manifest

Apply a graph8.app.yaml to this app.

Publishes the objects: block as a schema version through the same path POST /{app_id}/schema-versions uses, including the digest idempotency and the failure-isolated tenant fan-out, and stores frontend: / backend: as the build config a later deploy reads.

Refuses when the manifest's app.slug names a DIFFERENT app than the one in the path. Both halves of that mismatch are plausible mistakes -- a copied file, a wrong id in a script -- and either one silently applied would publish one app's schema into another app's tenants.

A manifest with no objects: publishes nothing. That is not an oversight: an empty schema would archive every object the app has ever declared across every consented tenant, so schema_publish refuses it, and a build-config only manifest is a legitimate thing to apply.