Add campaign UTM links and piha.li shortener as a core helper.

Keep mint/UTM in always-on core so email_sms and directmail stay optional, and brand utm_source from SITE_NAME (or UTM_SOURCE) instead of a hardcoded client name.
Closes westfarn/web_django_template#3

site/email_sms/services.py

@@ -23,6 +23,7 @@ from contacts.consent import (  # noqa: F401 — re-export for tests + providers
     unsubscribe_all,
 )
 from contacts.models import Channel, Contact
+from core.campaign_utm import ensure_campaign_utm_link
 from core.scheduling import parse_scheduled_for
 from email_sms.models import Campaign, Message, MessageTemplate
 
@@ -108,6 +109,17 @@ def create_campaign_draft(
         created_by=created_by,
         template=template,
     )
+    if channel in (Channel.EMAIL, Channel.SMS):
+        body = ensure_campaign_utm_link(
+            body,
+            name=name,
+            medium=channel,
+            html=(channel == Channel.EMAIL),
+            campaign_id=campaign.pk,
+        )
+        if body != campaign.body_override:
+            campaign.body_override = body
+            campaign.save(update_fields=["body_override", "updated_at"])
     contacts = list(opted_in_contacts(channel))
     Message.objects.bulk_create(
         [