File uploader: handle long filenames

Long filenames are not currently accounted for/handled in the file uploader:

<img width="445" height="512" alt="Image" src="https://github.com/user-attachments/assets/a5b133fa-0840-408f-a7c3-c98e4066f5d9" />

Reference: this Slack thread https://clickhouse-inc.slack.com/archives/C04U4FGNEH1/p1762876827463379