Email digest for followers #121
Description
Send a weekly email digest to users showing new articles from writers they follow and trending content.
Context: Passive readers need a pull mechanism to come back. Email is the most reliable re-engagement channel.
Acceptance criteria:
- Opt-in/out in user notification settings
- Weekly digest: new articles from followed writers + top trending
- Unsubscribe link in every email
- Can be powered by Inngest scheduled function (already in use)