Write the BEP for field-permission enforcement

BEP-1077 defines the field-permission model (role field_permissions, grant caps, effective fields = role list intersected with cap list); this BEP fixes how it is enforced. Decisions to settle: how lookup, querier, searcher and updater validate against the effective field set (blank on read, drop on update input, refuse filter/sort, natural-key lookup requiring READ on the key's field); at which layer an explicitly requested unpermitted GraphQL field is rejected and with what error; and the shape in which the resolved field set travels from the permission check into the specs (the validator-to-spec interface). Written against the BA-7593 tables. Korean draft first, then English, per the BEP workflow.

JIRA Issue: BA-7597

Start by reading BEP-1077 and the BA-7593 tables, then use the listed decisions to structure the BEP: effective-field validation for lookup, querier, searcher and updater, GraphQL rejection behavior, and the validator-to-spec field-set interface. Done means resolving these questions in a Korean draft first, followed by the English version under the BEP workflow.

Written by the indexing model from the issue text.