fix(auth): RP-initiated Keycloak logout + PKCE verifier race

Clicking logout previously only called supabase.auth.signOut(): Keycloak's
SSO cookie was untouched, so the (app) layout's $effect immediately
re-fired login() and Keycloak silently re-authenticated — logout looked
broken. That same chain also surfaced "PKCE code verifier not found in
storage" on prod, since signOut()'s async storage clear could race
signInWithOAuth()'s verifier write, or the $effect could double-fire and
overwrite verifiers mid-flight.

- logout(): signOut() then redirect to Keycloak's end_session endpoint
  (client_id + post_logout_redirect_uri=/logged-out). Keycloak shows a
  one-click "Do you want to log out?" confirmation because GoTrue's proxy
  flow does not expose the id_token, so we can't pass id_token_hint.
- isLoggingOut flag + guard in (app) layout $effect: prevents auto-relogin
  during the logout navigation.
- New public /logged-out route, outside the (app) group.
- A-05 rewritten, new A-07 (fresh login must prompt for credentials after
  RP-initiated logout).
- pgTAP 008 extended with 4 assertions for migration 014's UPDATE trigger.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/routes/(app)/+layout.svelte

@@ -2,7 +2,7 @@
 	import type { Snippet } from 'svelte';
 	import { page } from '$app/stores';
 	import { isAuthenticated, authLoading } from '$lib/stores/auth';
-	import { login } from '$lib/auth';
+	import { login, isLoggingOut } from '$lib/auth';
 	import DesktopSidebar from '$lib/components/layout/DesktopSidebar.svelte';
 	import MobileTopBar from '$lib/components/layout/MobileTopBar.svelte';
 	import BottomTabBar from '$lib/components/layout/BottomTabBar.svelte';
@@ -25,8 +25,11 @@
 	// When auth resolves as unauthenticated, redirect to Keycloak.
 	// This runs after onAuthStateChange fires (authLoading = false), so there
 	// is no race with Supabase's async localStorage initialisation.
+	// `isLoggingOut` suppresses re-login while logout() is mid-flight between
+	// signOut() and the Keycloak end-session redirect — otherwise we'd race
+	// the navigation and clobber the PKCE verifier.
 	$effect(() => {
-		if (!$authLoading && !$isAuthenticated) {
+		if (!$authLoading && !$isAuthenticated && !isLoggingOut) {
 			login();
 		}
 	});