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 #3

site/directmail/views.py

@@ -27,6 +27,7 @@ from directmail.providers.postcard.pcm import (
     list_designs,
 )
 from contacts.consent import opted_in_contacts
+from core.campaign_utm import utm_panel_context
 from core.scheduling import parse_scheduled_for
 from directmail.services import (
     create_campaign_draft,
@@ -58,8 +59,6 @@ _MAX_IMAGE_BYTES = 5 * 1024 * 1024
 def _audience_choices() -> list[tuple[str, str]]:
     """Labeled audience options with live opted-in counts."""
     rows = [
-        (Campaign.Audience.POSTCARD_OPT_IN, Channel.EMAIL, "email"),
-        (Campaign.Audience.SMS_OPT_IN, Channel.SMS, "SMS"),
         (Campaign.Audience.POSTCARD_OPT_IN, Channel.POSTCARD, "postcard"),
     ]
     choices = []
@@ -453,21 +452,13 @@ def campaign_list(request):
             form_errors.append("Campaign name is required.")
         if audience not in Campaign.Audience.values:
             form_errors.append("Choose a recipient list.")
-        if audience == Campaign.Audience.POSTCARD_OPT_IN:
+        elif audience == Campaign.Audience.POSTCARD_OPT_IN:
             if not template or template.channel != Channel.POSTCARD:
                 form_errors.append(
                     "Choose a postcard design (create one under Postcard design)."
                 )
             if not body:
                 body = "Postcard mailing"
-        else:
-            if not body:
-                form_errors.append("Body is required.")
-            if (
-                audience == Campaign.Audience.POSTCARD_OPT_IN
-                and not subject
-            ):
-                form_errors.append("Subject is required for email campaigns.")
 
         scheduled_for = None
         try:
@@ -505,6 +496,7 @@ def campaign_list(request):
             "form_data": form_data,
             "form_errors": form_errors,
             "image_upload_url": reverse("directmail:campaign_image_upload"),
+            **utm_panel_context(live=True, medium=Channel.POSTCARD),
         },
     )
 
@@ -528,6 +520,7 @@ def campaign_detail(request, pk):
             "recent_events": ctx["recent_events"],
             "events_title": ctx["events_title"],
             "events_empty": ctx["events_empty"],
+            **utm_panel_context(campaign=campaign, live=False),
             "can_send": campaign.status
             in {
                 Campaign.Status.DRAFT,