LAN admin on 10.0.0.128 plus quick campaign mint form (#12)

Closes #11.

## Summary
- Serve Django admin on LAN IP `10.0.0.128` (not `piha.li`). Compose now publishes `0.0.0.0:8005` and passes `SHORT_ADMIN_HOSTS` into the container.
- Admin index has a campaign mint form: domain, campaign, source, metric. Save builds `https://{domain}/?utm_campaign=&utm_source=&utm_medium=` (metric) and shows a copyable short URL.
- Public `/admin/` on `piha.lc` / `piha.li` stays 404.

## Test plan
- [ ] `cd site && uv run python manage.py test`
- [ ] Recreate compose (`docker compose up --build`) so `WEB_BIND` / `SHORT_ADMIN_HOSTS` take effect
- [ ] From another LAN machine: `http://10.0.0.128:8005/admin/` (staff login) shows the mint form
- [ ] Save a link for an allowlisted domain, copy the short URL, confirm it 302s
- [ ] `https://piha.li/admin` still 404

Reviewed-on: #12

site/links/templates/admin/index.html

@@ -0,0 +1,108 @@
+{% extends "admin/base_site.html" %}
+{% load i18n static admin_filters %}
+
+{% block extrastyle %}{{ block.super }}<link rel="stylesheet" href="{% static "admin/css/dashboard.css" %}" {% csp_nonce_attr %}>{% endblock %}
+
+{% block extrahead %}
+{{ block.super }}
+<script {% csp_nonce_attr %}>
+function copyShortUrl() {
+  var el = document.getElementById("id_short_url_result");
+  var btn = document.getElementById("copy-short-url");
+  if (!el) return;
+  var done = function () {
+    if (btn) {
+      btn.textContent = "Copied";
+      setTimeout(function () { btn.textContent = "Copy"; }, 1500);
+    }
+  };
+  if (navigator.clipboard && navigator.clipboard.writeText) {
+    navigator.clipboard.writeText(el.value).then(done, function () {
+      el.select();
+      document.execCommand("copy");
+      done();
+    });
+  } else {
+    el.select();
+    document.execCommand("copy");
+    done();
+  }
+}
+</script>
+{% endblock %}
+
+{% block coltype %}colMS{% endblock %}
+
+{% block bodyclass %}{{ block.super }} dashboard{% endblock %}
+
+{% block nav-breadcrumbs %}{% endblock %}
+
+{% block nav-sidebar %}{% endblock %}
+
+{% block content %}
+<div id="content-main" class="app-list">
+  <div class="module" id="quick-mint-module">
+    <h2>Create a short link</h2>
+    {% if created_link %}
+    <div class="form-row" style="padding: 12px 16px 0;">
+      <label for="id_short_url_result">Short URL</label>
+      <input id="id_short_url_result" type="text" readonly value="{{ created_link.public_short_url }}" size="48" style="max-width: 28rem;">
+      <button type="button" class="default" id="copy-short-url" onclick="copyShortUrl()">Copy</button>
+      <p class="help">Target: {{ created_link.target_url }}</p>
+    </div>
+    {% endif %}
+    <form method="post" action="{% url 'admin:index' %}" style="padding: 8px 16px 16px;">
+      {% csrf_token %}
+      {{ quick_mint_form.non_field_errors }}
+      <datalist id="allowed-domains">
+        {% for host in allowed_domains %}<option value="{{ host }}">{% endfor %}
+      </datalist>
+      {% for field in quick_mint_form %}
+      <div class="form-row">
+        {{ field.errors }}
+        <label for="{{ field.id_for_label }}">{{ field.label }}</label>
+        {{ field }}
+        {% if field.help_text %}<p class="help">{{ field.help_text }}</p>{% endif %}
+      </div>
+      {% endfor %}
+      <div class="submit-row">
+        <input type="submit" class="default" value="Save">
+      </div>
+    </form>
+  </div>
+  {% include "admin/app_list.html" with app_list=app_list show_changelinks=True %}
+</div>
+{% endblock %}
+
+{% block sidebar %}
+<div id="content-related">
+    <div class="module" id="recent-actions-module">
+        <h2>{% translate 'Recent actions' %}</h2>
+        <h3>{% translate 'My actions' %}</h3>
+            {% load log %}
+            {% get_admin_log 10 as admin_log for_user user %}
+            {% if not admin_log %}
+            <p>{% translate 'None available' %}</p>
+            {% else %}
+            <ul class="actionlist">
+            {% for entry in admin_log %}
+            <li class="{% if entry.is_addition %}addlink{% endif %}{% if entry.is_change %}changelink{% endif %}{% if entry.is_deletion %}deletelink{% endif %}">
+                <span class="visually-hidden">{% if entry.is_addition %}{% translate 'Added:' %}{% elif entry.is_change %}{% translate 'Changed:' %}{% elif entry.is_deletion %}{% translate 'Deleted:' %}{% endif %}</span>
+                {% if entry.is_deletion or not entry.get_admin_url %}
+                    {{ entry.object_repr|to_object_display_value }}
+                {% else %}
+                    <a href="{{ entry.get_admin_url }}">{{ entry.object_repr|to_object_display_value }}</a>
+                {% endif %}
+                <br>
+                {% if entry.content_type %}
+                    <span class="mini quiet">{% filter capfirst %}{{ entry.content_type.name }}{% endfilter %}</span>
+                {% else %}
+                    <span class="mini quiet">{% translate 'Unknown content' %}</span>
+                {% endif %}
+            </li>
+            {% endfor %}
+            </ul>
+            {% endif %}
+    </div>
+</div>
+{% endblock %}