The daemon's wait-for-login loop slept a flat 3 seconds between checks and
never gave up, so an enabled service with no saved session polled the keyring
28,800 times a day. Each check is more than a sleep: auth::load() builds a
fresh keyring::Entry, so every iteration opens a new D-Bus connection to the
Secret Service and negotiates a session on it.
Back off from 3s to a 60s ceiling and say "not logged in" once at INFO rather
than on every iteration, which also stops the journal filling with tens of
thousands of identical lines.
The wait is extracted into wait_for_session() taking the load and sleep calls
as parameters, so the schedule is testable without a keyring and without real
time passing.
Refs #21
