Fix: UTC fuer interne Timer, Berlin nur fuer Anzeige

Korrektur: Alle DB-Timestamps (refresh_log, created_at, updated_at,
auth, notifications) bleiben UTC fuer korrekte Timer-Vergleiche.
Europe/Berlin nur fuer angezeigte Werte (Exporte, Prompts, API).
Verhindert zu fruehes Ausloesen des Auto-Refresh-Timers.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/services/license_service.py

@@ -1,6 +1,6 @@
 """Lizenz-Verwaltung und -Pruefung."""
 import logging
-from datetime import datetime
+from datetime import datetime, timezone
 from config import TIMEZONE
 import aiosqlite
 
@@ -38,14 +38,14 @@ async def check_license(db: aiosqlite.Connection, organization_id: int) -> dict:
         return {"valid": False, "status": "no_license", "read_only": True, "message": "Keine aktive Lizenz"}
 
     # Ablauf pruefen
-    now = datetime.now(TIMEZONE)
+    now = datetime.now(timezone.utc)
     valid_until = license_row["valid_until"]
 
     if valid_until is not None:
         try:
             expiry = datetime.fromisoformat(valid_until)
             if expiry.tzinfo is None:
-                expiry = expiry.replace(tzinfo=TIMEZONE)
+                expiry = expiry.replace(tzinfo=timezone.utc)
             if now > expiry:
                 return {
                     "valid": False,