Add shopper accounts, reviews, tracking, and seed_demo (#10)

## Summary
- Closes #9. Port shop-gated buyer accounts (register/login/profile, password reset, order history), purchase-gated reviews, and Stripe customer ids. Cards stay on Stripe.
- Slim public contact form to email + interest + message. Shipping tracking status, scan events, paste-in numbers, and EasyPost webhook when FEATURE_SHIPPING is on.
- Add template-neutral `seed_demo` (generic SKUs, demo shoppers, guest orders, tracking stubs). Prod refused. `--reset` deletes tagged demo rows after invoices.

## Test plan
- [ ] `cd site && uv run python manage.py test` (173 tests passed locally)
- [ ] Shop on: `/account/register`, login, profile, password reset, claim guest orders by email
- [ ] Shop off: `/account/` URLs absent; Sign in / Account links hidden
- [ ] Checkout as logged-in buyer stores `Order.user` and Stripe customer id; product review only after paid purchase
- [ ] Shipping on: portal paste-in tracking + EasyPost webhook updates status; shipping off: orders still work without tracking UI
- [ ] `seed_demo` refused in prod; `--reset` rebuilds tagged catalog/shoppers without deleting staff invoices

Reviewed-on: #10

site/shipping/templates/shipping/detail.html

@@ -3,8 +3,52 @@
 {% block topbar_title %}{{ shipment.order.number }}{% endblock %}
 {% block portal_content %}
 <p>{{ shipment.order.email }} · {{ shipment.get_status_display }}</p>
-{% if shipment.tracking_number %}<p>Tracking: {{ shipment.tracking_number }}</p>{% endif %}
+{% if shipment.tracking_number %}
+<p>
+  Tracking: {{ shipment.tracking_number }}
+  {% if shipment.tracking_status %} · {{ shipment.get_tracking_status_display }}{% endif %}
+</p>
+{% if shipment.tracking_url %}<p><a href="{{ shipment.tracking_url }}" target="_blank" rel="noopener">Track package</a></p>{% endif %}
+<form method="post" action="{% url 'shipping:shipment_refresh_tracking' shipment.pk %}">
+  {% csrf_token %}
+  <button class="btn btn-ghost btn-sm" type="submit">Refresh tracking</button>
+</form>
+{% endif %}
 {% if shipment.label_url %}<p><a href="{{ shipment.label_url }}">Download label</a></p>{% endif %}
+
+<h3>Add tracking</h3>
+<p class="hint-block">Paste a number from Pirate Ship or the carrier. EasyPost looks up scan events when an API key is set.</p>
+<form method="post" action="{% url 'shipping:shipment_attach_tracking' shipment.pk %}">
+  {% csrf_token %}
+  <div class="form-grid">
+    <div class="field">
+      <label for="id_tracking_number">Tracking number</label>
+      <input id="id_tracking_number" name="tracking_number" value="{{ shipment.tracking_number }}" required>
+    </div>
+    <div class="field">
+      <label for="id_carrier">Carrier</label>
+      <input id="id_carrier" name="carrier" value="{{ shipment.carrier }}" placeholder="USPS, UPS, FedEx">
+    </div>
+  </div>
+  <button class="btn btn-primary" type="submit">Save tracking</button>
+</form>
+
+{% if shipment.tracking_events %}
+<h3>Scan history</h3>
+<table class="table">
+  <thead><tr><th>When</th><th>Status</th><th>Detail</th></tr></thead>
+  <tbody>
+    {% for event in shipment.tracking_events %}
+    <tr>
+      <td>{{ event.datetime }}</td>
+      <td>{{ event.status }}</td>
+      <td>{{ event.message }}{% if event.location %} · {{ event.location }}{% endif %}</td>
+    </tr>
+    {% endfor %}
+  </tbody>
+</table>
+{% endif %}
+
 {% if shipment.status != 'labeled' %}
 <form method="post" action="{% url 'shipping:shipment_buy' shipment.pk %}">
   {% csrf_token %}