docs(auth): add SSO documentation and test credentials

- Document cross-domain SSO with COOKIE_DOMAIN configuration
- Add production test credentials for automated testing
- Explain cookie-based SSO flow across *.mana.how subdomains

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

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

@@ -16,7 +16,7 @@
 	import {
 		isSidebarMode as sidebarModeStore,
 		isNavCollapsed as collapsedStore,
-	} from '$lib/stores/navigation';
+	} from '$lib/stores/navigation.svelte';
 	import { PillNavigation } from '@manacore/shared-ui';
 	import type { PillNavItem, PillDropdownItem } from '@manacore/shared-ui';
 	import { getPillAppItems } from '@manacore/shared-branding';