feat(subscribe): queue Weeztix coupon, then Mailwizz; document queues

- RegisterSubscriberOnPage: persist subscriber then dispatch integrations
- IssueWeeztixCouponForSubscriber on weeztix queue; dispatches Mailwizz after
  coupon attempt (idempotent if coupon_code already set); failed() fallback
- SyncSubscriberToMailwizz implements ShouldQueueAfterCommit
- Deployment: worker listens weeztix,mailwizz,default; warn against sync in prod
- .env.example: QUEUE_CONNECTION notes for subscribe UX

Made-with: Cursor

.env.example

@@ -45,6 +45,10 @@ SESSION_DOMAIN=null
 
 BROADCAST_CONNECTION=log
 FILESYSTEM_DISK=local
+
+# Use "database" or "redis" in production and run `php artisan queue:work` (see documentation/DEPLOYMENT-STRATEGY.md).
+# Avoid "sync" in production: Mailwizz (and Weeztix coupon) jobs would run inside the HTTP request; a thrown error
+# can return 5xx to the visitor even though the subscriber row is already saved — confusing UX.
 QUEUE_CONNECTION=database
 
 CACHE_STORE=database