Prereq for SB-10 (POST /api/consent/ai). Append-only per-user audit
trail of AI-processing consent grants. The iOS app posts a fresh row
whenever the user opts in to off-device AI flows during onboarding or
via Settings; a revoke + re-grant cycle mints fresh rows so the
timeline reads chronologically and the latest non-revoked row per
(user, kind) is the source of truth for "is AI active right now".
Backs both App-Store Guideline 5.1.2(i) ("data-collection consent must
be verifiable") and the GDPR Art. 7 documentation burden. The server
persists the raw signed artefact (PDF receipt or signed JWT — caller's
choice) without parsing it; the audit trail is the storage itself plus
the `signed_at` wall-clock the client recorded.
Migration 0074 is additive only; IF NOT EXISTS guards mirror 0067 /
0070 / 0071. No table rewrite, no breaking change.
Marc-André Bombeck
c9d5479b0d