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/hooks.py

@@ -1,5 +1,6 @@
 from core.registry import (
     register_dashboard_collector,
+    register_dispatcher,
     register_feature,
     register_portal_nav,
 )
@@ -15,6 +16,7 @@ def register() -> None:
         order=50,
     )
     register_dashboard_collector(_dashboard)
+    register_dispatcher(_sync_tracking)
 
 
 def _dashboard(request) -> dict:
@@ -29,3 +31,9 @@ def _dashboard(request) -> dict:
         .exclude(pk__in=labeled)
         .count()
     }
+
+
+def _sync_tracking() -> int:
+    from shipping.services import sync_open_tracking
+
+    return sync_open_tracking()