docs(UAT_PLAYBOOK): document rbac auto-provision pre-condition for Better-Auth customers (GRO-2052)

QA review (PR #143) flagged UAT_PLAYBOOK.md update as the blocking item.
Adds a Pre-conditions sub-section covering TC-API-3.16/3.19a/b/c: test
users must have a Better-Auth 'user' row so resolveStaffMiddleware
auto-provisions a 'groomer' staff row before pets.ts runs the owner-bypass.

Includes a SQL verification query and the pre-fix 403 symptom to aid UAT
debugging.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

UAT_PLAYBOOK.md

@@ -40,6 +40,24 @@ CUSTOMER=$(kubectl get secret seed-uat-passwords -n groombook-uat \
 
 **How to apply:** at the start of every UAT run that touches TC-API-1.4 / 1.5 / 1.6 / 1.7 / 3.18 / 3.21 / 3.23, refresh these four env vars from the cluster before issuing the sign-in request.
 
+### rbac auto-provision for Better-Auth customers (GRO-2052)
+
+> Applies to TC-API-3.16 / 3.19a / 3.19b / 3.19c (customer-as-owner profile-summary paths) and any future case where the test user authenticates via Better-Auth email/password and the route relies on `resolveStaffMiddleware` to resolve a `staff` row.
+
+**Pre-condition (rbac auto-provision):** The test user must have a row in the Better-Auth `user` table (email/password sign-in creates this automatically — see TC-API-1.6 / 1.7). On first authenticated call, `resolveStaffMiddleware` (`./src/middleware/rbac.ts`) auto-provisions a `groomer` staff row keyed by `staff.user_id = user.id` (Better-Auth branch fires before the legacy OIDC `account` branch).
+
+**Verify the auto-provision fired** by querying the DB after the first authenticated call:
+
+```sql
+SELECT user_id, role FROM staff WHERE user_id = '<test-user-id>';
+```
+
+Expected: one row, `role = 'groomer'`. If zero rows return, the request hit the OIDC `account` branch and 403'd, or the user has no `user` row — fix the test sign-in path before re-running.
+
+**Why this matters:** without the auto-provision branch, Better-Auth email/password customers (e.g. `uat-customer@groombook.dev`) have no `account` row for the OIDC providers, so `resolveStaffMiddleware` falls through to `403 "Forbidden: no staff record found for authenticated user"` *before* `pets.ts` can run the owner-bypass added in GRO-2013. The owner-bypass code is unreachable unless the auto-provision has fired. A green TC-API-3.19a therefore implicitly proves the auto-provision worked; if 3.19a fails with the pre-fix 403, the auto-provision branch is missing from the deployed `./src` tree (see [GRO-2052](/GRO/issues/GRO-2052)).
+
+**How to apply:** for every run of TC-API-3.16 / 3.19a / 3.19b / 3.19c, sign in via TC-API-1.6 (email+password) first to guarantee the `user` row exists, then run the profile-summary call, then assert the `staff` row above before declaring pass.
+
 ## Test Cases
 
 ### 4.0 Health Check