feat(lib): subscription content ingestion adapter — BYO-license master updates into firm libraries

[thewrz]

Context

ADR-019 affirms BYO-license content ingestion: firms with their own subscription to a master-content or standards-reference service connect credentials and pull updates into their own libraries (ADR-015) with origin_meta provenance. Per-firm entitlement; SpecR never redistributes ingested content.

Scope

Create (per adapter, after a research spike):

• Adapter seam following the ADR-014 plug-in philosophy applied to content sources
• Ingested content lands in firm-owned libraries with origin_meta provenance

Acceptance

• Defined per adapter at spike time; license-compliance bar per ADR-019 Consequences is mandatory

Out of scope

Any specific provider adapter before its research spike; bundling content with SpecR (ADR-019).