fix(web): add mouse/touch subfolder navigation in open project dialog

[jesperordrup]

Fixes #13853

Summary

• add an explicit chevron action in the Open Project dialog to descend into subfolders with mouse/touch
• keep row selection behavior unchanged so clicking a row still selects the folder
• add ArrowRight support as a keyboard alternative to Tab for descending into subfolders

Testing

• not run locally (UI-only change)

[github-actions]

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