corrige zona horaria en votación: TZ=America/Santiago en contenedor

El contenedor corría en UTC causando que la ventana horaria no
coincidiera con la hora local. Se agrega TZ en docker-compose y se
muestra la hora actual del servidor en el panel de votación.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/routers/admin.py

@@ -244,6 +244,7 @@ def voting_admin(request: Request, db: Session = Depends(get_db)):
             "config": config,
             "results": results,
             "total_votes": total_votes,
+            "server_time": datetime.now().strftime("%H:%M:%S"),
             "error": None,
             "success": None,
         },
@@ -261,6 +262,8 @@ def update_voting_config(
     _require_admin(request)
     config = _get_or_create_config(db)
 
+    now_str = datetime.now().strftime("%H:%M:%S")
+
     try:
         datetime.strptime(start_time, "%H:%M")
         datetime.strptime(end_time, "%H:%M")
@@ -273,6 +276,7 @@ def update_voting_config(
                 "config": config,
                 "results": results,
                 "total_votes": sum(r["votes"] for r in results),
+                "server_time": now_str,
                 "error": "Formato de hora inválido. Use HH:MM",
                 "success": None,
             },
@@ -288,6 +292,7 @@ def update_voting_config(
                 "config": config,
                 "results": results,
                 "total_votes": sum(r["votes"] for r in results),
+                "server_time": now_str,
                 "error": "La hora de inicio debe ser anterior a la hora de fin",
                 "success": None,
             },
@@ -307,6 +312,7 @@ def update_voting_config(
             "config": config,
             "results": results,
             "total_votes": sum(r["votes"] for r in results),
+            "server_time": now_str,
             "error": None,
             "success": "Configuración guardada",
         },