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/shop/admin.py

@@ -1,6 +1,6 @@
 from django.contrib import admin
 
-from shop.models import Order, OrderItem, Product
+from shop.models import Order, OrderItem, Product, ProductReview
 
 
 @admin.register(Product)
@@ -11,6 +11,13 @@ class ProductAdmin(admin.ModelAdmin):
     prepopulated_fields = {"slug": ("name",)}
 
 
+@admin.register(ProductReview)
+class ProductReviewAdmin(admin.ModelAdmin):
+    list_display = ("product", "user", "rating", "created_at")
+    list_filter = ("rating",)
+    search_fields = ("product__name", "user__email", "title")
+
+
 class OrderItemInline(admin.TabularInline):
     model = OrderItem
     extra = 0
@@ -21,4 +28,5 @@ class OrderAdmin(admin.ModelAdmin):
     list_display = ("number", "email", "amount", "status", "created_at")
     list_filter = ("status",)
     search_fields = ("number", "email", "customer_name")
+    raw_id_fields = ("user",)
     inlines = [OrderItemInline]