- Add syncIdentities() to auth store to propagate identity changes from
identity store, fixing stale data that caused save failures and duplicates
- Call syncIdentities() after every create, update, and delete in the
identity manager modal
- Switch email composer to read identities from identity store for
consistency with the rest of the app
- Append identity text signature (with RFC 3676 separator) to email body
when sending from the composer and quick reply paths
- Add tests for syncIdentities and signature appending logic