Extends the harness to the money/notification replay invariants
(previously only asserted by app code / manual audit):
- stripe_webhook_events PK -> a retried Stripe event id is rejected
(replay protection).
- member_billing UNIQUE(space_id,member_id) -> the webhook's
onConflict upsert never duplicates a member's billing row.
- notifications UNIQUE(space_id,dedupe_key) + ON CONFLICT DO NOTHING
-> a replayed enqueue collapses to exactly one outbox row.
21 integration tests green on real Postgres; default pnpm test
unaffected (hermetic); build clean. Non-runtime.
