feat(notifications+admin): marketing campaigns

- campaigns table (migration 19) + CRUD + send endpoint in notification-svc
- audience resolution reads cross-schema from identity.users (all / verified /
  with_plan); send dispatches via the SMS or Email channel and logs deliveries
- endpoints: GET/POST /v1/campaigns, POST /v1/campaigns/:id/send, DELETE
- gateway route /v1/campaigns/* → notification
- /admin/marketing: create campaign (channel, audience, template/subject/body),
  list with status + sent counts, send, delete

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/notification/cmd/server/main.go

@@ -40,6 +40,7 @@ func main() {
 	prefH := handlers.NewPreferenceHandler(store)
 	tplH := handlers.NewTemplateHandler(store)
 	chH := handlers.NewChannelHandler(store)
+	campH := handlers.NewCampaignHandler(store)
 
 	r := gin.Default()
 
@@ -93,6 +94,12 @@ func main() {
 	v1.POST("/sms/send", auth, admin, chH.SendSMS)
 	v1.POST("/email/send", auth, admin, chH.SendEmail)
 
+	// ── Marketing campaigns (admin) ───────────────────────────────────────────
+	v1.GET("/campaigns", auth, admin, campH.List)
+	v1.POST("/campaigns", auth, admin, campH.Create)
+	v1.POST("/campaigns/:id/send", auth, admin, campH.Send)
+	v1.DELETE("/campaigns/:id", auth, admin, campH.Delete)
+
 	// ── Internal: create notification (service-to-service) ───────────────────
 	v1.POST("/internal/notifications", serviceAuth, notifH.CreateInternal)