Add event-specific guest gift reservations endpoint

Introduced a function `get_event_guest_gift_reservations` in the CRUD layer to fetch gift reservations filtered by event ID. Updated the API endpoint to optionally accept an `event_id` query parameter for retrieving reservations specific to an event.

backend/app/crud/gift.py

@@ -387,6 +387,41 @@ class CRUDGiftPurchase(CRUDBase[GiftPurchase, GiftPurchaseCreate, GiftPurchaseUp
 
         return result
 
+    def get_event_guest_gift_reservations(self, db: Session, event_id: UUID | str) -> List[GiftPurchase]:
+        """Retrieve all gift reservations for guests belonging to a specific event."""
+        event_id = event_id if isinstance(event_id, UUID) else UUID(event_id)
+
+        stmt = (
+            select(Guest)
+            .where(Guest.event_id == event_id)
+            .options(joinedload(Guest.gifts))
+        )
+
+        # Correct: Call unique() on the RESULT, not on the stmt
+        guests = db.execute(stmt).unique().scalars().all()
+
+        results = []
+        for guest in guests:
+            for gift in guest.gifts:
+                reservation_stmt = select(GuestGifts).where(
+                    (GuestGifts.c.guest_id == guest.id) &
+                    (GuestGifts.c.gift_id == gift.id)
+                )
+
+                reservation = db.execute(reservation_stmt).first()
+
+                if reservation:
+                    purchase = GiftPurchase(
+                        id=UUID('00000000-0000-0000-0000-000000000000'),
+                        gift_id=gift.id,
+                        guest_id=guest.id,
+                        quantity=1,
+                        purchased_at=reservation.reserved_at,
+                        notes=reservation.notes
+                    )
+                    results.append(purchase)
+
+        return results
 
 # Create CRUD instances
 gift_item_crud = CRUDGiftItem(GiftItem)