refactor: replace Optional[X] with X | None for Python 3.10+ compatibility

Co-authored-by: Neiland85 <164719485+Neiland85@users.noreply.github.com>

Author: Copilot

app/routers/operator.py

@@ -1,5 +1,4 @@
 from fastapi import APIRouter, Depends, Path
-from typing import Optional
 from pydantic import BaseModel, Field
 
 from app.auth.dependencies import get_current_user_flexible, verify_api_key
@@ -295,7 +294,7 @@ async def invoice(
     invoice_id: str = Path(
         ..., description="ID de la factura a generar", examples=["INV-2025-789012"]
     ),
-    data: Optional[InvoiceRequest] = None,
+    data: InvoiceRequest | None = None,
     _current_user: User | None = current_user_flexible_dep,
 ) -> InvoiceResponse:
     """