Issue #5876 - Fix filename conflict issue by appending numbers in parentheses

[junnzhuu]

This PR resolves issue #5876 by modifying the filename conflict resolution. Previously, numbers were appended directly to filenames which could alter their meaning. Now, the numbers are enclosed in parentheses to avoid changing the original meaning.

Changes made:

• Modified findUniqueFileName in UploadWorker.kt to append sequence numbers in parentheses.
• Updated regular expression handling to support filenames with and without extensions.

Tested the changes with multiple uploads, and filenames are now correctly generated.