L17 Pakete: Stufen Basis/Profi, Lotse-Chat-Plätze und Kontingent

- Datenmodell: Tenant.tier (Default PROFI), lotseChatSeats, lotseChatHardLimit;
  Tabelle lotse_chat_seats (RLS, TENANT_MODELS, pii-fields), Index für die
  Monatszählung der Chat-Nachrichten (Migration 20260921100000_pakete)
- src/lib/plans.ts: Stufenregeln, 150 Chats je Platz, Mehrverbrauch in 100er-Paketen
- src/server/plan.ts: effektive Freischaltung = Stufe UND TenantModule, genutzt von
  requireModule, assertModuleEnabled, API, Sync (Offline-Op → rejected mit Klartext),
  Navigation, isLotseEnabled und planningAccess (Planung nur in Profi)
- Lotse-Chat: Platzprüfung (no_seat), Testphase ohne Platz, Kontingent mit
  hartem Limit (quota_exhausted); Platzvergabe durch den Mandanten-Admin
- Betreiber: Stufe/Plätze/hartes Limit im Mandantendetail mit Bestätigung
  und Plattform-Audit, Verbrauch laufender Monat/Vormonat, Stufe als Badge
- Demo-Seed: demo = Profi mit 3 Plätzen, demo2 = Basis
- Tests: test-pakete-{rules,gates,seats}

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

messages/en/offline.json

@@ -92,7 +92,9 @@
     "internal": "Technical error – will retry automatically.",
     "timeOverlap": "The added time overlaps with time already recorded and was not accepted.",
     "timeWindow": "The added time is outside the allowed 7 days, in the future or too long and was not accepted.",
-    "otherSession": "Time was still running on another order – the start was not accepted. Please start again and switch."
+    "otherSession": "Time was still running on another order – the start was not accepted. Please start again and switch.",
+    "notInPlan": "Included in the Profi package – not activated for this company. The entry was not applied, please contact the office.",
+    "moduleDisabled": "This function is switched off for this company. The entry was not applied, please contact the office."
   },
   "view": {
     "title": "Offline view",