Add meaningful domain events to the 8 gRPC services (account
add/update/remove/probe, mark-read, sync dispatch, contact create,
rule create/update/delete/import/export, triage, export, audit verify),
instrument the previously-silent send/calendar_sync/contacts_sync
routines, log outbox mutation attempt+result at the executor decision
level, and trace every graceful-shutdown drain step plus the
ShuttingDown event emission. Domain events inherit the OBS-2 per-RPC
span (request_id) rather than duplicating its entry/exit lines. Only
ids, counts, transport/op/rule kinds, folder names, and status are
logged -- never bodies, subjects, addresses, credentials, or tokens.
Refs #359
James Maes