New files created via the "+" button were not appearing in the file tree
because visibleFilePaths was derived solely from bundle API data. The
selection reset effect would also immediately undo the file selection.
Add pendingFiles state to track newly created files until they are saved
to disk. Include pending files in visibleFilePaths, guard the selection
reset effect, and clean up pending state after successful save.
Fixes PAP-563
Co-Authored-By: Paperclip <noreply@paperclip.ing>
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