Add shopper accounts, reviews, tracking, and seed_demo (#9)

Closes #9. Shop-gated buyer accounts, purchase reviews, Stripe customer ids, shipment tracking, slim public contact form, and a template-neutral seed_demo command.

site/shop/templates/shop/detail.html

@@ -15,6 +15,47 @@
       <label>Qty <input name="quantity" type="number" min="1" value="1"></label>
       <button class="button button-primary" type="submit">Add to cart</button>
     </form>
+    <h2>Reviews</h2>
+    {% if review_count %}
+    <p>{{ review_avg|floatformat:1 }} / 5 · {{ review_count }} review{{ review_count|pluralize }}</p>
+    {% else %}
+    <p>No reviews yet.</p>
+    {% endif %}
+    {% if can_review %}
+    <form method="post" action="{% url 'shop:review' product.slug %}">
+      {% csrf_token %}
+      <p>
+        <label for="review-rating">Rating</label>
+        <select id="review-rating" name="rating" required>
+          <option value="">Choose 1–5</option>
+          <option value="5">5 — Excellent</option>
+          <option value="4">4 — Good</option>
+          <option value="3">3 — Okay</option>
+          <option value="2">2 — Fair</option>
+          <option value="1">1 — Poor</option>
+        </select>
+      </p>
+      <p><label>Title (optional) <input name="title" maxlength="120"></label></p>
+      <p><label>Review (optional) <textarea name="body" rows="4"></textarea></label></p>
+      <button class="button button-primary" type="submit">Submit review</button>
+    </form>
+    {% elif already_reviewed %}
+    <p>You already reviewed this product.</p>
+    {% elif user.is_authenticated %}
+    <p>Buy this product to leave a review.</p>
+    {% else %}
+    <p><a href="{% url 'account:login' %}?next={{ request.path }}">Sign in</a> after a purchase to leave a review.</p>
+    {% endif %}
+    <ul>
+      {% for review in reviews %}
+      <li>
+        <strong>{{ review.rating }}/5</strong>
+        {% if review.title %} · {{ review.title }}{% endif %}
+        <span> — {{ review.user.first_name|default:review.user.email }}</span>
+        {% if review.body %}<p>{{ review.body|linebreaks }}</p>{% endif %}
+      </li>
+      {% endfor %}
+    </ul>
   </div>
 </section>
 {% endblock %}