NotificationSlackSender runs after the emailer: core SendMessageAction to the
configured provider (default "slack") with user:<id>, no qbit-slack import.
Pause and quiet hours apply (CRITICAL bypasses quiet hours), SECURITY sends
title and link only, daily digest DMs, SKIPPED without a provider or on a
user-facing refusal. Supersedes the 2026-10-13 "Slack never per user"
decision (owner, 2026-10-14; QRun-IO/qbit-slack DESIGN section 10).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
slackMode and slackMinSeverity on alerts_notification_preference;
slackStatus and slackMessageId on alerts_notification_recipient.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>