fix: Correct datetime format for SQLite seeding

backend/app/main.py

@@ -62,7 +62,7 @@ async def startup_event():
                     description="Large scale ERP for hospital network.",
                     buyer="Servicio de Salud",
                     status="Publicada",
-                    closing_date=(datetime.now() + timedelta(days=15)).strftime("%Y-%m-%d"),
+                    closing_date=datetime.now() + timedelta(days=15),
                     estimated_amount=450000000,
                     region="Metropolitana",
                     sector="Software",
@@ -74,7 +74,7 @@ async def startup_event():
                     description="Machine learning and predictive models.",
                     buyer="Subsecretaría de Prevención del Delito",
                     status="Publicada",
-                    closing_date=(datetime.now() + timedelta(days=10)).strftime("%Y-%m-%d"),
+                    closing_date=datetime.now() + timedelta(days=10),
                     estimated_amount=180000000,
                     region="Nacional",
                     sector="AI & Software",
@@ -86,7 +86,7 @@ async def startup_event():
                     description="24/7 monitoring and incident response.",
                     buyer="Ministerio del Interior",
                     status="Publicada",
-                    closing_date=(datetime.now() + timedelta(days=5)).strftime("%Y-%m-%d"),
+                    closing_date=datetime.now() + timedelta(days=5),
                     estimated_amount=320000000,
                     region="Metropolitana",
                     sector="Cybersecurity",
@@ -98,7 +98,7 @@ async def startup_event():
                     description="Migration of legacy systems to AWS/Azure.",
                     buyer="Tesorería General",
                     status="Publicada",
-                    closing_date=(datetime.now() + timedelta(days=25)).strftime("%Y-%m-%d"),
+                    closing_date=datetime.now() + timedelta(days=25),
                     estimated_amount=120000000,
                     region="Valparaíso",
                     sector="Cloud",