fix: ensure all timestamps use UTC timezone

- Add NowFunc to GORM config for UTC auto-generated timestamps
- Add .UTC() to all time.UnixMilli() calls in trader files
- Add .UTC() to all time.Now() calls in store and api files
- Fix TypeScript unused imports in frontend

store/strategy.go

@@ -328,7 +328,7 @@ func (s *StrategyStore) Update(strategy *Strategy) error {
 			"config":         strategy.Config,
 			"is_public":      strategy.IsPublic,
 			"config_visible": strategy.ConfigVisible,
-			"updated_at":     time.Now(),
+			"updated_at":     time.Now().UTC(),
 		}).Error
 }