docs(stripe): document Phase 9.1 blocked status and live-mode readiness checklist

New: PHASE9_1_STRIPE_TEST_VALIDATION.md — baseline verification, the exact Stripe-credential
search performed (none found), the Stripe architecture review (dynamic price_data, unchanged),
what was proven vs. blocked per the mission's own step list, and the live-mode readiness
checklist. Updated: STRIPE_INTEGRATION_RUNBOOK.md and WINTER_BREAK_LAUNCH_CHECKLIST.md to point
at the new opt-in test and the blocked status. PHASE9_COMMERCE_AND_LAUNCH.md gets a short
addendum. No application code changed this phase — no genuine defect was exposed without real
Stripe traffic, so no regression rerun was required.

docs/PHASE9_COMMERCE_AND_LAUNCH.md

@@ -271,6 +271,12 @@ Real Stripe live-mode validation once credentials exist (`docs/STRIPE_INTEGRATIO
 text once reviewed; and, informed by real Winter Break Camp commercial operation, whether a
 waitlist is actually worth building.
 
+**Phase 9.1 addendum**: real Stripe TEST-mode validation was attempted immediately after this
+phase and remained blocked on the exact same missing credentials — see `docs/
+PHASE9_1_STRIPE_TEST_VALIDATION.md`. That phase added a permanent, opt-in integration test
+(`platform/test/stripe-integration-test.js`, default no-op, refuses live-mode keys) ready to run
+the real proof the moment `STRIPE_SECRET_KEY`/`STRIPE_WEBHOOK_SECRET` (test mode) exist.
+
 ---
 
 ## PHASE 9 APPLICATION BUILD COMPLETE / LIVE STRIPE VALIDATION PENDING