Feature: More explicit BIP39 watch only wallet

> I would rather better / more explicitly implement in the front end a BIP39 watch only wallet then putting this in the Electrum device category.

I agree with this point. (This is essentially [new_device_manual.jinja](https://github.com/cryptoadvance/specter-desktop/blob/master/src/cryptoadvance/specter/templates/device/new_device_manual.jinja) )

_Originally posted by @relativisticelectron in https://github.com/cryptoadvance/specter-desktop/issues/1622#issuecomment-1106416951_

Start with src/cryptoadvance/specter/templates/device/new_device_manual.jinja, which the issue identifies as the relevant front-end entry point. Trace how the device category is presented and make the BIP39 watch-only wallet explicit rather than placing it in the Electrum device category; done means the front end clearly distinguishes this wallet type.

Written by the indexing model from the issue text.