Support for differentiating between signing and viewing keys

At present, the Cycles FE differentiates between the signing (Keplr) and viewing keys (ephemeral key generated in-browser).

Quartz does not yet support this differentiation.

This is necessary as part of Cycles Demo 2 to support reading encrypted set-offs back from the chain.

Start by reading the Quartz implementation and the Cycles FE behavior described in the issue, focusing on how signing and viewing keys are currently represented. Trace the path needed to read encrypted set-offs back from the chain and identify the relevant tests or entry points. Done means Quartz differentiates both key types for Cycles Demo 2.

Written by the indexing model from the issue text.