docs: partner provisioning API contract, routing context, Track P

A partner integration request landed for programmatic merchant-hierarchy
management (Company/Project/Store/PaymentPoint). Built the answer generically:
partner-specific behaviour is a PartnerProfile config row, and no partner name
appears in any entity, field, endpoint or status value.

New:
- docs/backend/PARTNER-PROVISIONING-API-CONTRACT.md - hierarchy, idempotency,
  node-scoped public-key credentials, TEST/LIVE partition, routing context
- docs/context/adrs/ADR-0003-generic-partner-provisioning-api.md

Amended, because the schema impact must land before Phase 1 is implemented:
- Phase 1 gains RoutingContext on CheckoutSession/PaymentIntent/Payment,
  frozen at checkout-session creation and immutable after
- Phase 7 gains routing on Refund/ReconciliationRecord, plus the rule that
  seller settlement splits happen after routing, never as a hierarchy level
- Phase 9 gains Company/Project above Marketplace and PaymentPoint below it,
  with a backfill sequence for existing marketplaces
- Track S gains partner credentials: public key only, node-scoped authority,
  rotation with overlap, immediate revoke, audit coverage

Also: Track P (P1-P10) in the delivery plan, and backend ownership closed as
answered across the contract set.

Card payment was checked, not added - qr and card both already ship in
cart.component.ts with separate create paths and status pollers.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/PRODUCT-PLAN-v3.1-GAP-ANALYSIS.md

@@ -255,7 +255,7 @@ Not gaps — assets and risks they should know about before sequencing:
 
 See [PRODUCT-PLAN-v3.1-DELIVERY-PLAN.md](PRODUCT-PLAN-v3.1-DELIVERY-PLAN.md) Sprint 0.1 for the full record and downstream consequences. Summary:
 
-1. **Backend ownership — still open.** First-pass question wasn't understood; needs re-asking in plain terms before Phase 1 implementation (not just contract-writing) starts.
+1. **Backend ownership — answered 2026-08-18.** A separate backend developer implements against `docs/backend/`. This repository owns the frontend and the contract set.
 2. **Payment chain — unfrozen. Yes.** Phases 1, 6, 7 proceed.
 3. **External marketplaces — no fixed list.** Connectors onboard partners as they arrive; build the Phase 4 framework config-driven/generic, not per-named-provider.
 4. **FX rate source — ours, in-house, as a safety gate.** No external provider committed; backend computes FX authoritatively until/unless one is chosen later.