iOS/Android - Pending receipt lost when signing out mid-upload; save to gallery before storage is cleared

[MelvinBot]

Problem

When a user signs out on iOS/Android while a receipt is still queued for upload (e.g. offline), the pending receipt is lost.

Solution

If a user signs out while a receipt is still uploading, save that receipt image to the device gallery before storage is cleared, and show a confirmation modal with the prompt.

Context

Follow-up from #92139.

[rinej]

Follop up PR -> #97562