Keep attribution storage richer than filter UX

Reusable design lesson from Shield PR #723 / COR-3895 review: when product UX narrows to one “Created via” filter, keep canonical creator/source/provider attribution for persistence, audit, display, API, and exports, but remove creator/provider facet state and predicates. Reduce the database facet to one access-scoped GROUP BY on resolved source and support multi-select with set membership. Avoid rewriting a channel field such as externalSource merely to make historical provider facets work; that conflates orthogonal dimensions. Provenance: read-only review of e3-solutions/theft PR #723 against origin/staging on 2026-09-03.