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/urls.py

@@ -8,6 +8,17 @@ urlpatterns = [
     path("", views.shipment_list, name="shipment_list"),
     path("new/", views.shipment_create, name="shipment_create"),
     path("export/pirate-ship.csv", views.pirate_ship_export, name="pirate_ship_export"),
+    path("webhooks/easypost/", views.easypost_webhook, name="easypost_webhook"),
     path("<uuid:pk>/", views.shipment_detail, name="shipment_detail"),
     path("<uuid:pk>/buy/", views.shipment_buy, name="shipment_buy"),
+    path(
+        "<uuid:pk>/tracking/",
+        views.shipment_attach_tracking,
+        name="shipment_attach_tracking",
+    ),
+    path(
+        "<uuid:pk>/tracking/refresh/",
+        views.shipment_refresh_tracking,
+        name="shipment_refresh_tracking",
+    ),
 ]