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/STRIPE_INTEGRATION_RUNBOOK.md

@@ -74,8 +74,13 @@ test).
 
 ## Local testing against real Stripe TEST mode (once credentials exist)
 
-Not yet exercised in this repo — no Stripe account/credentials have been provided as of this
-phase. Once they exist:
+Not yet exercised in this repo — no Stripe account/credentials have been provided as of Phase
+9.1 either (see `docs/PHASE9_1_STRIPE_TEST_VALIDATION.md` for the exact search performed and
+what's needed). Once they exist, `platform/test/stripe-integration-test.js` (added in Phase 9.1)
+automates most of the steps below — set `RUN_STRIPE_INTEGRATION_TEST=true` plus
+`STRIPE_SECRET_KEY`/`STRIPE_WEBHOOK_SECRET`/`OWNER_EMAIL`/`OWNER_PASSWORD` and run it; it refuses
+to run against a live-mode key and makes zero Stripe network calls unless explicitly enabled.
+Manually, or to understand what that script does:
 
 1. Create (or use an existing) Stripe account, switch to **Test mode** in the dashboard.
 2. Copy the test-mode **Secret key** (`sk_test_...`) into `STRIPE_SECRET_KEY`.