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>

services/notification/cmd/server/main.go

@@ -39,6 +39,7 @@ func main() {
 	notifH := handlers.NewNotificationHandler(store)
 	prefH := handlers.NewPreferenceHandler(store)
 	tplH := handlers.NewTemplateHandler(store)
+	chH := handlers.NewChannelHandler(store)
 
 	r := gin.Default()
 
@@ -86,6 +87,12 @@ func main() {
 	v1.GET("/notification-templates", auth, admin, tplH.List)
 	v1.PUT("/notification-templates", auth, admin, tplH.Upsert)
 
+	// ── Channels: SMS (Kavenegar) + Email (SMTP) config & send (admin) ────────
+	v1.GET("/channels", auth, admin, chH.ListConfigs)
+	v1.PUT("/channels/:channel", auth, admin, chH.UpsertConfig)
+	v1.POST("/sms/send", auth, admin, chH.SendSMS)
+	v1.POST("/email/send", auth, admin, chH.SendEmail)
+
 	// ── Internal: create notification (service-to-service) ───────────────────
 	v1.POST("/internal/notifications", serviceAuth, notifH.CreateInternal)