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/directmail/templates/directmail/campaign_detail.html

@@ -1,4 +1,5 @@
 {% extends "portal_base.html" %}
+{% load static %}
 {% block title %}{{ campaign.name }} · Campaign{% endblock %}
 {% block topbar_title %}{{ campaign.name }}{% endblock %}
 {% block portal_content %}
@@ -51,6 +52,13 @@
 </div>
 {% endif %}
 
+<div class="panel" style="margin-bottom:16px">
+  <div class="panel-h"><h2>Tracked site link</h2></div>
+  <div class="panel-b">
+    {% include "core/_utm_link_panel.html" with utm_live=False utm_medium=campaign.channel utm_campaign_name=campaign.name %}
+  </div>
+</div>
+
 <div class="stat-row" id="campaign-stats">
   <div class="stat-card">
     <div class="label">Messages</div>
@@ -208,7 +216,10 @@
 </div>
 {% endblock %}
 {% block extra_js %}
+<script src="https://cdn.jsdelivr.net/npm/qrcode@1.5.4/build/qrcode.min.js"></script>
+<script src="{% static 'js/campaign-utm.js' %}"></script>
 <script>
+window.CampaignUtm.bindPanel(document.getElementById("utm-link-panel"));
 (function () {
   var panel = document.getElementById("recipients-panel");
   var page = (panel && panel.getAttribute("data-page")) || "1";

site/directmail/templates/directmail/campaign_list.html

@@ -1,4 +1,5 @@
 {% extends "portal_base.html" %}
+{% load static %}
 {% block title %}Campaigns · Portal{% endblock %}
 {% block topbar_title %}Campaign composer{% endblock %}
 {% block extra_head %}
@@ -64,6 +65,7 @@
           <label for="id_name">Campaign name</label>
           <input id="id_name" name="name" type="text" required
                  placeholder="Spring seller tips" value="{{ form_data.name }}">
+          <div class="hint">Used as <code>utm_campaign</code> on the tracked site link.</div>
         </div>
         <div class="field" id="subject-field">
           <label for="id_subject">Subject</label>
@@ -128,6 +130,7 @@
           </div>
         </div>
         <p class="hint-block">Saves a draft campaign and recipient stubs. Send from the campaign report when ready. You’ll get an email when the send finishes.</p>
+        {% include "core/_utm_link_panel.html" with utm_live=True utm_medium="postcard" %}
         <button class="btn btn-primary" type="submit">Save draft</button>
       </form>
     </div>
@@ -179,6 +182,8 @@
 {% endblock %}
 {% block extra_js %}
 <script src="https://cdn.jsdelivr.net/npm/quill@2.0.3/dist/quill.js"></script>
+<script src="https://cdn.jsdelivr.net/npm/qrcode@1.5.4/build/qrcode.min.js"></script>
+<script src="{% static 'js/campaign-utm.js' %}"></script>
 <script>
 (function () {
   var uploadUrl = "{{ image_upload_url|escapejs }}";
@@ -283,6 +288,8 @@
       var active = (ch === 'email' && isEmail) || (ch === 'sms' && isSms) || (ch === 'postcard' && isPostcard);
       a.classList.toggle('active', active);
     });
+    var panel = document.getElementById('utm-link-panel');
+    if (panel && panel._utmApply) panel._utmApply();
     syncCampaignPreview();
   };
 
@@ -370,6 +377,13 @@
   if (tmplSelect) tmplSelect.addEventListener('change', syncCampaignPreview);
 
   initQuill();
+  window.CampaignUtm.bindPanel(document.getElementById('utm-link-panel'), {
+    getName: function () {
+      return (document.getElementById('id_name') || {}).value || '';
+    },
+    getMedium: function () { return 'postcard'; },
+    csrfToken: csrfToken
+  });
   syncComposeChannel();
 })();
 </script>