feat: Auto-seed admin user on container start

- prestart.sh: runs seed_admin.py after migrations
- seed_admin.py: reads ADMIN_EMAIL and ADMIN_PASSWORD from env vars
- Creates default tenant + admin role + admin user if not exists

scripts/seed_admin.py

@@ -69,12 +69,12 @@ async def seed():
             print(f"Admin role exists: {role.id}")
 
         # Check if admin user exists
-        result = await db.execute(select(User).where(User.email == "admin@media-on.de"))
+        result = await db.execute(select(User).where(User.email == os.environ.get("ADMIN_EMAIL", "admin@media-on.de")))
         user = result.scalar_one_or_none()
 
         if user is None:
             user = User(
-                email="admin@media-on.de",
+                email=os.environ.get("ADMIN_EMAIL", "admin@media-on.de"),
                 name="Administrator",
                 password_hash=hash_password(os.environ.get("ADMIN_PASSWORD", "Admin123!")),
                 is_active=True,