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>

src/app/[locale]/admin/layout.tsx

@@ -25,6 +25,7 @@ export default async function AdminLayout({
     { href: "/admin/files", label: t("media") },
     { href: "/admin/ai", label: t("aiContent") },
     { href: "/admin/messaging", label: t("messaging") },
+    { href: "/admin/marketing", label: t("marketing") },
     { href: "/admin/users", label: t("users") },
     { href: "/admin/plans", label: t("plans") },
     { href: "/admin/discounts", label: t("discounts") },