feat(notifications+admin): SMS (Kavenegar) + Email (SMTP) channels & templates

Backend (notification-svc):
- channel_config table (per-tenant Kavenegar + SMTP settings) + migration 18
- sender pkg: Kavenegar SMS client + SMTP mailer (STARTTLS / implicit TLS), stdlib only
- endpoints: GET/PUT /v1/channels[/:channel], POST /v1/sms/send, POST /v1/email/send
  (template + {{var}} rendering); deliveries logged
- seeded 3 Persian email templates: welcome / account_verification / promotion
- gateway routes /v1/{channels,sms,email}/* → notification

Admin UI:
- /admin/messaging: SMS + Email provider config cards, test-send, email template editor
- nav link + fa/en labels

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

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

@@ -24,6 +24,7 @@ export default async function AdminLayout({
     { href: "/admin/slides", label: t("slides") },
     { href: "/admin/files", label: t("media") },
     { href: "/admin/ai", label: t("aiContent") },
+    { href: "/admin/messaging", label: t("messaging") },
     { href: "/admin/users", label: t("users") },
     { href: "/admin/plans", label: t("plans") },
     { href: "/admin/discounts", label: t("discounts") },

src/app/[locale]/admin/messaging/page.tsx

@@ -0,0 +1,7 @@
+"use client";
+
+import { MessagingAdmin } from "@/components/admin/MessagingAdmin";
+
+export default function Page() {
+  return <MessagingAdmin />;
+}