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/models.py

@@ -17,3 +17,19 @@ class RealtorProfile(TimeStampedModel):
 
     def __str__(self) -> str:
         return self.display_name or self.user.get_username()
+
+
+class CustomerProfile(TimeStampedModel):
+    """Shop-buyer profile. Card numbers stay on Stripe; we only keep the customer id."""
+
+    user = models.OneToOneField(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="customer_profile",
+    )
+    phone = models.CharField(max_length=32, blank=True)
+    shipping_address = models.JSONField(default=dict, blank=True)
+    stripe_customer_id = models.CharField(max_length=255, blank=True)
+
+    def __str__(self) -> str:
+        return self.user.get_username()