Drawing a barré should not clear mute/open state of string on fretboard diagrams (and vice versa)

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

Currently, when in barré entry mode in fretboard diagram properties, clicking once on the diagram will draw a barré from that point all the way to the rightmost string, resetting any open/muted string markers already set above the diagram immediately. The opposite is also true: changing the string state clears any barrés on that string

This is undesirable in some cases, like if you intentionally set the rightmost string to O (for open) and want to draw a partial barré excluding that string. You have to go back and set O again after drawing the barré.

Steps:

1. Add a fretboard diagram
2. Click above the rightmost string to draw an O
3. Check the barré box on
4. Click on the first fret
5. See that the O is erased

Supporting files, videos and screenshots

https://github.com/user-attachments/assets/ff0d5f96-3b42-4246-82e9-54a3a93aba60

What is the latest version of MuseScore Studio where this issue is present?

Nightly

Regression

No.

Operating system

macOS 15

Additional context

No response

Checklist

• This report follows the guidelines for reporting bugs and issues
• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
• I have attached all requested files and information to this report
• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible