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

.env.prod.example

@@ -73,6 +73,14 @@ OLLAMA_BASE_URL=http://10.0.0.128:11434
 OLLAMA_MODEL=llama3.2
 OLLAMA_TIMEOUT_SECONDS=120
 
+# Required in beta/prod when FEATURE_EMAIL_SMS or FEATURE_DIRECT_MAIL is on.
+# POST /api/links/ on the API host. Recipients hit https://piha.li/<code>.
+# Token must match SHORTENER_API_TOKENS on url_shortening_service (name:secret).
+# Generate: python -c "import secrets; print(secrets.token_urlsafe(32))"
+SHORTENER_BASE_URL=https://shortener.aimloperations.com
+SHORTENER_API_TOKEN=acme:replace-me
+# UTM_SOURCE=acme  # optional; default is a slug of SITE_NAME
+
 NOMINATIM_BASE_URL=http://10.0.0.128:8089
 NOMINATIM_TIMEOUT_SECONDS=8
 NOMINATIM_COUNTRY_CODES=us
@@ -90,3 +98,5 @@ GUNICORN_BIND=0.0.0.0:8000
 # PUBLIC_SITE_URL=https://example-preview.aimloperations.com
 # DATABASE_URL=postgres://westfarn:replace-db-password@10.0.0.230:5432/client_site_beta
 # WEB_PORT=8014
+# SHORTENER_BASE_URL=https://shortener-beta.aimloperations.com
+# SHORTENER_API_TOKEN=acme:replace-with-a-different-token