Social recovery via dark crystal

In settings, allow use of dark crystal for sharding and sharing seed phrase among friends (social recovery)

MVP: user and friends must all have MetaMask accounts

libraries:
https://github.com/blockades/scuttle-dark-crystal
https://github.com/blockades/dark-crystal-secrets

related to #1292

Start by reviewing the scuttle-dark-crystal and dark-crystal-secrets libraries, then read related issue #1292 for existing context. Trace how settings currently handle wallet recovery and define the MVP flow for MetaMask users and friends to shard, share, and recover a seed phrase. Done means the scope, security behavior, and recovery flow are specified and tested.

Written by the indexing model from the issue text.