Add entropy into vault generation

We removed the text field for entropy, but we should collect entropy from somewhere when creating a vault, maybe mouse movements, or key timing during password entry, something.

Curious for ideas on other good entropy sources on someone's computer @christianlundkvist

Start by tracing the vault-creation flow where the entropy text field was removed and reviewing how password entry is handled. The issue names no files or tests and asks for ideas, so define the acceptable entropy source and completion criteria with maintainers before implementation.

Written by the indexing model from the issue text.