feat(DATA-003): calculate live option greeks

app/pages/overview.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from datetime import UTC, datetime
+from datetime import datetime, timezone
 
 from nicegui import ui
 
@@ -20,7 +20,7 @@ def _format_timestamp(value: str | None) -> str:
         timestamp = datetime.fromisoformat(value.replace("Z", "+00:00"))
     except ValueError:
         return value
-    return timestamp.astimezone(UTC).strftime("%Y-%m-%d %H:%M:%S UTC")
+    return timestamp.astimezone(timezone.utc).strftime("%Y-%m-%d %H:%M:%S UTC")
 
 
 def _build_live_portfolio(config: PortfolioConfig, quote: dict[str, object]) -> dict[str, float | str]: