Analytics aggregation

Mailgun webhook /api/email/webhooks/mailgun (already exists) currently handles delivered/bounce. Extend to consume: opened, clicked, complained, unsubscribed.

For each event:

1. Look up Campaign.mailgunId (stored at send time).

2. Resolve CampaignLog by (campaignId, subscriberId) — Mailgun event payload includes recipient + message-id -> tag mapping.

3. Set the matching boolean + timestamp column on CampaignLog.

4. Recompute the per-campaign rollups on Campaign (opened, clicked, bounced, ...) using:

   const rollup = await prisma.campaignLog.groupBy({
     by: ['campaignId'],
     where: { campaignId },
     _count: { opened: true, clicked: true, bounced: true, delivered: true, unsubscribed: true, complained: true },
   })
   await prisma.campaign.update({ where: { id: campaignId }, data: {
     opened: rollup[0]._count.opened, clicked: rollup[0]._count.clicked, bounced: rollup[0]._count.bounced,
     delivered: rollup[0]._count.delivered, unsubscribed: rollup[0]._count.unsubscribed, complained: rollup[0]._count.complained,
   }})
   

5. Subscribe to Mailgun event types: delivered, opened, clicked, bounced, complained, unsubscribed (via dashboard or POST /v3/domains/{domain}/webhooks/{hookid}).

Engagement rollups on Subscriber (emailsOpened, linksClicked, lastOpenedAt, lastClickedAt) can be updated in the same handler keyed off subscriberId.