Confirm before clearing recent projects

[BenJule]

Summary

• add a confirmation dialog before clearing all recent projects
• make No the default choice to prevent accidental deletion
• leave removal of individual recent projects unchanged

Testing

• ran git diff --check
• verified the Clear All confirmation control flow
• verified that the dialog only appears for the empty-filename Clear All action
• no local full build; the change is limited to the existing recent-project handler

Fixes #8351