Notification email templates (Novu workflows)

In-app notifications are Beta and native; email is fake-backed — Novu is stood up with ZERO workflows and today a send logs failed. Scope: author the 13 per-kind email workflows on Novu using the 21 platform-default email templates shipped in Templates slice 1, prove one real send per kind, and wire per-user notification preferences. Wave 0 content work (market-audit decision #5).