Get Notification Prefs

What TaxCompass may email this account about (AP-115).

One field today, and it is a whole preference rather than a patch: a PUT states the resulting state. The field is therefore required — an omitted key would otherwise fall back to the default and silently re-enable a channel the user had just switched off, which is the one failure mode an opt-out must not have. The digest's own idempotency stamp (users.last_digest_at) is deliberately absent: it is the sender's bookkeeping, not something a user sets.