Mint campaign UTM links through the piha.li shortener.

Closes #9.

Auto-insert tracked homepage links in campaign compose, register them with
url_shortening_service, and put short piha.li URLs in SMS, email hrefs, and
postcard QR codes when SHORTENER_* is configured.

.env.example

@@ -79,6 +79,14 @@ SOCIAL_TOKEN_ENCRYPTION_KEY=
 OLLAMA_BASE_URL=http://10.0.0.128:11434
 OLLAMA_MODEL=llama3.2
 
+# URL shortener (piha.li). Empty locally = long UTM URLs in campaigns.
+# Call the API host, never https://piha.li (that host only 302s).
+SHORTENER_BASE_URL=
+SHORTENER_API_TOKEN=
+# Local shortener compose:
+# SHORTENER_BASE_URL=http://127.0.0.1:8005
+# SHORTENER_API_TOKEN=monica:dev-only-token
+
 # Nominatim (LAN) — address autocomplete via Django /api/address-suggest/
 # Nominatim has no built-in API keys; optional NOMINATIM_API_KEY only if you
 # put a gateway in front that checks X-API-Key.