* ios: delete temp data from storage view
The temp folder is the XFTP agent work directory and holds scratch
files for received-file encryption and roster transfers, so deleting it
under a running chat breaks those writes mid-flight. The button is only
enabled while chat is stopped, the same precondition core deleteStorage
relies on, and the row says how to stop chat.
* ios: show delete temp data alert over settings sheet
AlertManager presents from ContentView, which is behind the settings
sheet, so the confirmation never appeared. The alert now also warns
that interrupted transfers never complete and that videos in unsent
drafts, which live in the temp folder, are lost, and the caption names
the screen where chat is stopped.
* ios: say unsent draft videos are sent without the file
A draft video whose converted file was deleted from the temp folder is
still sent, as a preview with no file, so "lost" understated it.
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Co-authored-by: Evgeny Poberezkin <evgeny@poberezkin.com>
