Iteration 1: Auth (lokale Accounts), RBAC, RLS-Policies, i18n

- Auth.js v5 mit Credentials-Provider: Argon2id-Verifikation, JWT-Session
  mit Mandanten-Kontext, Rollen und Permissions; Login-/Logout-Flow (deutsch)
- RBAC-Katalog (28 Permissions, 5 Rollen-Blueprints) mit serverseitigem
  requirePermission; Seed legt Demo-Mandant und 4 Demo-Nutzer an
- Route-Gate über Next-16-proxy.ts (UX-Ebene), autoritative Prüfung
  serverseitig via requireSession/requirePermission
- Prisma-Migrationen: init + Row-Level-Security-Policies (zweite
  Verteidigungslinie, Scharfschaltung in Härtungs-Iteration dokumentiert)
- i18n-Gerüst mit next-intl (de aktiv, en vorbereitet), Audit-Log-Helper
- Login/Logout end-to-end im Browser verifiziert; Build/Lint/Typecheck grün

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

messages/en.json

@@ -0,0 +1,23 @@
+{
+  "common": {
+    "appName": "ISMS Tool",
+    "logout": "Sign out"
+  },
+  "login": {
+    "title": "Sign in",
+    "subtitle": "Sign in with your company account.",
+    "email": "E-mail address",
+    "password": "Password",
+    "tenant": "Organization (optional)",
+    "tenantHint": "Only needed if your e-mail exists in several organizations.",
+    "submit": "Sign in",
+    "error": "Sign-in failed. Please check e-mail, password and organization."
+  },
+  "dashboard": {
+    "title": "Dashboard",
+    "welcome": "Welcome, {name}",
+    "tenant": "Tenant",
+    "roles": "Roles",
+    "placeholder": "Module dashboards (risks, tasks, SoA coverage) follow in upcoming iterations."
+  }
+}