The RenameFileDialog is always mounted (MUI Dialog does not unmount
children when closed), so useState(filename) only captures the
initial value on first mount. Because the dialog initially mounts
with an empty filename, every subsequent open showed a stale empty
input rather than the current file path.

Track the previous filename prop and reset pathValue during render
when it changes, following the React 'adjusting state during render'
pattern instead of useEffect.