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/accounts/admin.py

@@ -1,9 +1,16 @@
 from django.contrib import admin
 
-from accounts.models import RealtorProfile
+from accounts.models import CustomerProfile, RealtorProfile
 
 
 @admin.register(RealtorProfile)
 class RealtorProfileAdmin(admin.ModelAdmin):
     list_display = ("user", "display_name", "phone")
     search_fields = ("user__username", "display_name")
+
+
+@admin.register(CustomerProfile)
+class CustomerProfileAdmin(admin.ModelAdmin):
+    list_display = ("user", "phone", "stripe_customer_id")
+    search_fields = ("user__username", "user__email", "phone", "stripe_customer_id")
+    readonly_fields = ("stripe_customer_id",)