Feature Request: Allow Multiple Last Used Denominations When Sending

**Motivation**
Currently, when sending a Bitcoin amount tied to a fiat value, users can only select one fiat currency from the sending screen. To switch—say from USD to EUR—you have to return to the main menu, which takes around 10 taps and requires re-entering the recipient’s address. This process is time-consuming and frustrating, especially for users who frequently switch currencies.

**Proposed Solution**
Update the denomination shortcut list on the sending screen to reflect currencies and units last used by the user.

For example, if a user regularly switches between USD, EUR, GBP, BTC, sats, and CAD, those should be remembered and accessible directly from the sending screen.

Currently:
• The app offers 5 fixed Bitcoin unit options: BTC, mBTC, µBTC, bits, and sats.
• But only one fiat currency can be selected at a time.

By allowing multiple recently used fiat currencies (alongside BTC units) to persist in the shortcut list, the experience becomes much more flexible. Users who frequently switch between fiat and non-default Bitcoin units will benefit from faster, smoother transactions.