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/position_builder.go

@@ -69,8 +69,8 @@ func (pb *PositionBuilder) handleOpen(
 			Status:             "OPEN",
 			Source:             "sync",
 			Fee:                fee,
-			CreatedAt:          time.Now(),
-			UpdatedAt:          time.Now(),
+			CreatedAt:          time.Now().UTC(),
+			UpdatedAt:          time.Now().UTC(),
 		}
 		return pb.positionStore.CreateOpenPosition(position)
 	}