Add campaign UTM links and piha.li shortener (#4)

## Summary
- Port Monica campaign UTM + piha.li minting into always-on `core` (`shortener.py`, `campaign_utm.py`) so `email_sms` and `directmail` stay optional and never import each other.
- `utm_source` is a slug of `SITE_NAME` (override with `UTM_SOURCE`). Email gets an HTML `data-campaign-utm` link; SMS gets a plain URL; postcard QR only — no body inject.
- Live composer mints through login+CSRF `POST /portal/campaigns/short-link/` (registered only when an outreach app is installed). Empty `SHORTENER_*` falls back to the long UTM URL.

Reference: [monica_site PR #10](ai_ml_operations/monica_site#10)

Closes #3

## Test plan
- [x] `cd site && uv run python manage.py test` (125 tests)
- [ ] Email composer: type a name, confirm HTML link + `utm_campaign` updates, save draft
- [ ] SMS composer: plain `piha.li` (or long UTM if shortener unset) in the body
- [ ] Postcard composer: QR copies the tracked URL; campaign body has no `utm_source`
- [ ] Campaign report pages show the same panel
- [ ] With `FEATURE_EMAIL_SMS` and `FEATURE_DIRECT_MAIL` off, no extra nav and no `/portal/campaigns/short-link/` route

Reviewed-on: #4

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(
         [