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/client_site/urls.py

@@ -5,7 +5,7 @@ from django.contrib import admin
 from django.urls import include, path
 
 from contacts.views import address_suggest
-from core.views import healthz
+from core.views import campaign_short_link, healthz
 
 urlpatterns = [
     path("healthz/", healthz, name="healthz"),
@@ -24,6 +24,14 @@ if apps.is_installed("email_sms"):
     urlpatterns += [path("portal/messaging/", include("email_sms.urls"))]
 if apps.is_installed("directmail"):
     urlpatterns += [path("portal/direct-mail/", include("directmail.urls"))]
+if apps.is_installed("email_sms") or apps.is_installed("directmail"):
+    urlpatterns += [
+        path(
+            "portal/campaigns/short-link/",
+            campaign_short_link,
+            name="campaign_short_link",
+        ),
+    ]
 if apps.is_installed("blog"):
     urlpatterns += [
         path("blog/", include("blog.public_urls")),