Integrate payjoin session persistence into workflow

Integrate payjoin session persistence into workflow

Wire the payjoin persistence layer into the existing send and receive
flows so session state is saved during normal operation and can be
replayed later. Initialize the database from the handlers, replace
the noop persisters with SQLite-backed persisters, resume existing
sessions, and record seen inputs in the receiver flow for replay
protection.

This moves persistence from a standalone storage layer into the
runtime payjoin workflow so interrupted sessions can continue from
saved state instead of starting over. It also simplifies error
handling by relying on `?` once the storage errors map cleanly into
the CLI error type.