Promote uat → main (PROD): GRO-2358 logout on no-access screen (#74)

Promote uat → main (PROD): GRO-2358 — restore logout on 'Portal access not configured' screen.

Squashed from uat-to-main/GRO-2358 (0d24fe0).

Cherry-pick of validated uat squash bfe3ccf.

Pre-merge gates green: CI (Lint+Typecheck 30s, Test 23s, Docker Build 11s); CTO Gitea review APPROVED (comment 13465); QA GRO-2362 done; UAT GRO-2363 4/4 PASS on git.farh.net/groombook/web:2026.06.11-bfe3ccf; Security GRO-2364 cleared.

Head branch uat-to-main/GRO-2358 retained for Flea's post-deploy verification.

Refs GRO-2358, GRO-2362, GRO-2363, GRO-2364, GRO-2367.

Co-authored-by: Flea Flicker <22+gb_flea@noreply.git.farh.net>
Co-committed-by: Flea Flicker <22+gb_flea@noreply.git.farh.net>

src/portal/CustomerPortal.tsx

@@ -15,6 +15,7 @@ import { ImpersonationBanner } from "./ImpersonationBanner.js";
 import { AuditLogViewer } from "./AuditLogViewer.js";
 import { useBranding } from "../BrandingContext.js";
 import { getDevUser } from "../pages/DevLoginSelector.js";
+import { signOut } from "../lib/auth-client.js";
 import type { ImpersonationSession } from "@groombook/types";
 import type { Appointment as PortalAppointment } from "./sections/Appointments.js";
 
@@ -193,6 +194,19 @@ export function CustomerPortal() {
     }
   }, [session]);
 
+  // Shared sign-out handler — wires the canonical Better Auth `signOut()` so
+  // every authenticated surface (no-access screen, portal chrome, etc.) uses
+  // the same implementation as `AdminLayout`. Failure to reach the server
+  // still leaves the SPA free to navigate to /login.
+  const handleSignOut = useCallback(async () => {
+    try {
+      await signOut();
+    } catch {
+      // Best-effort; navigate to /login regardless so the user is never trapped.
+    }
+    window.location.href = "/login";
+  }, []);
+
   const logPageView = useCallback((page: string) => {
     if (!session) return;
     void fetch(`/api/impersonation/sessions/${session.id}/log`, {
@@ -281,14 +295,7 @@ export function CustomerPortal() {
             <h1 className="text-lg font-semibold text-stone-800 mb-2">Portal access not configured</h1>
             <p className="text-sm text-stone-600 mb-6">{authError}</p>
             <button
-              onClick={async () => {
-                try {
-                  await fetch("/api/auth/sign-out", { method: "POST", credentials: "include" });
-                } catch {
-                  // Best-effort sign-out; redirect to /login regardless.
-                }
-                window.location.href = "/login";
-              }}
+              onClick={() => { void handleSignOut(); }}
               className="inline-flex items-center justify-center gap-2 px-4 py-2 rounded-lg text-sm font-medium text-stone-700 bg-stone-100 hover:bg-stone-200 transition-colors"
             >
               <LogOut size={14} />