Fix: Rename directory to remove & character causing shell issues

Renamed ebook_backend&admin_panel to ebook_backend_admin_panel
  The & character was being interpreted by shell as background
  process operator, causing 'Dockerfile not found' errors in Coolify.

ebook_backend_admin_panel/admin-backend/models/coupon.py

@@ -0,0 +1,22 @@
+from sqlalchemy import Column, Integer, String, DateTime
+from datetime import datetime
+import pytz
+from utils.auth import Base
+
+class Coupon(Base):
+    """
+    SQLAlchemy model representing a coupon code entry in the database.
+
+    Attributes:
+        id (int): Primary key identifier.
+        code (str): Unique coupon code string.
+        usage_count (int): Number of times the coupon has been used.
+        created_at (datetime): Timestamp of coupon creation (stored in Europe/Bratislava timezone).
+        used_at (datetime | None): Timestamp of the last usage, nullable.
+    """
+    __tablename__ = "coupon_codes"
+    id = Column(Integer, primary_key=True)
+    code = Column(String, unique=True)
+    usage_count = Column(Integer, default=0)
+    created_at = Column(DateTime, default=lambda: datetime.now(pytz.timezone('Europe/Bratislava')))
+    used_at = Column(DateTime, nullable=True)