Short term storage expiration does not take into account "exporting time"

When we export something using the `ShortTermStorageManager`, it will be deleted automatically after a fixed duration (usually 24h). However, in some cases, depending on the size of the data exported, the export process itself may take hours, and then the expiration will trigger shortly after.

To calculate the expiration time, we should probably use the "finalization time" instead of the "creation time" of the export.

Start by locating ShortTermStorageManager and the export finalization path. Trace how the expiration time is calculated, then verify that a long-running export remains available for the configured duration after finalization, including with a focused test.

Written by the indexing model from the issue text.