Add a shop sales dashboard with 30-day charts (#4)

## Summary
- Closes #3
- Portal Retail **Sales** page: 30-day orders/revenue/units/AOV, daily charts, top products
- Home dashboard cards for 30-day shop sales and revenue
- Stacks on #2. Merge that first, then retarget `master` if needed.

## Test plan
- [ ] Sales page requires login; empty state with no paid orders
- [ ] Paid/fulfilled in the last 30 days counted; unpaid/old excluded
- [ ] Home dashboard shows 30-day sales count
- [ ] `manage.py test shop`

Reviewed-on: #4

site/shop/tests.py

@@ -1,4 +1,5 @@
 import struct
+from datetime import timedelta
 from decimal import Decimal
 from io import BytesIO
 from pathlib import Path
@@ -13,10 +14,11 @@ from django.core.files.uploadedfile import SimpleUploadedFile, TemporaryUploaded
 from django.db import models
 from django.test import Client, TestCase, override_settings
 from django.urls import reverse
+from django.utils import timezone
 from PIL import Image
 
 from core.models import StoredFile
-from shop.models import Order, Product, ProductColor, ProductImage
+from shop.models import Order, OrderItem, Product, ProductColor, ProductImage
 from shop.services import (
     ShopError,
     add_to_cart,
@@ -29,6 +31,7 @@ from shop.services import (
     store_product_image,
     store_product_stl,
 )
+from shop.stats import sales_dashboard
 
 def _tiny_png() -> bytes:
     image = Image.new("RGBA", (8, 8), (200, 40, 40, 255))
@@ -591,3 +594,108 @@ class ShopPortalTests(TestCase):
         self.assertFalse(tmp_path.exists())
         self.assertEqual(bytes(stored.data), _tiny_stl())
         self.assertEqual(stored.kind, StoredFile.Kind.PRODUCT_STL)
+
+
+def _sold_order(product, *, qty=1, paid_at=None, status=None, number=None):
+    n = Order.objects.count() + 1
+    order = Order.objects.create(
+        number=number or f"ORD-TEST-{n:04d}",
+        email=f"buyer{n}@example.com",
+        customer_name="Pat",
+        status=status or Order.Status.PAID,
+        amount=product.price * qty,
+        currency="usd",
+        paid_at=paid_at if paid_at is not None else timezone.now(),
+    )
+    OrderItem.objects.create(
+        order=order,
+        product=product,
+        name=product.name,
+        sku=product.sku,
+        quantity=qty,
+        unit_price=product.price,
+    )
+    return order
+
+
+class ShopSalesDashboardTests(TestCase):
+    def setUp(self):
+        User = get_user_model()
+        self.user = User.objects.create_user("merchant", password="test-pass-123")
+        self.client = Client()
+        self.client.login(username="merchant", password="test-pass-123")
+        self.dragon = _product(name="Dragon", sku="DRAGON", price=Decimal("18.00"))
+        self.fox = _product(name="Fox", sku="FOX", price=Decimal("12.00"))
+
+    def test_sales_requires_login(self):
+        anon = Client()
+        self.assertEqual(anon.get(reverse("shop_portal:sales")).status_code, 302)
+
+    def test_empty_dashboard(self):
+        data = sales_dashboard()
+        self.assertEqual(data["order_count"], 0)
+        self.assertEqual(data["revenue"], Decimal("0.00"))
+        self.assertEqual(len(data["daily_sales"]), 30)
+        self.assertFalse(data["has_sales"])
+        response = self.client.get(reverse("shop_portal:sales"))
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(response, "No paid orders in this window")
+        self.assertContains(response, "Sales")
+        self.assertContains(response, "Orders per day")
+        self.assertContains(response, "Top products")
+
+    def test_counts_paid_and_fulfilled_in_window(self):
+        now = timezone.now()
+        _sold_order(self.dragon, qty=2, paid_at=now)
+        _sold_order(self.fox, qty=5, paid_at=now - timedelta(days=2))
+        _sold_order(
+            self.dragon,
+            qty=1,
+            paid_at=now - timedelta(days=1),
+            status=Order.Status.FULFILLED,
+        )
+        _sold_order(
+            self.fox,
+            qty=9,
+            paid_at=now - timedelta(days=40),
+        )
+        open_order = _sold_order(self.dragon, qty=3, paid_at=None, status=Order.Status.OPEN)
+        open_order.paid_at = None
+        open_order.save(update_fields=["paid_at"])
+        cancelled = _sold_order(
+            self.fox, qty=4, paid_at=now, status=Order.Status.CANCELLED
+        )
+        self.assertEqual(cancelled.status, Order.Status.CANCELLED)
+
+        data = sales_dashboard()
+        self.assertEqual(data["order_count"], 3)
+        self.assertEqual(data["units_sold"], 8)
+        self.assertEqual(data["revenue"], Decimal("114.00"))
+        self.assertEqual(data["aov"], Decimal("38.00"))
+        self.assertEqual([row["sku"] for row in data["top_products"]], ["FOX", "DRAGON"])
+        self.assertEqual(data["top_products"][0]["units"], 5)
+        self.assertEqual(data["top_products"][1]["units"], 3)
+        today_bar = data["daily_sales"][-1]
+        self.assertEqual(today_bar["count"], 1)
+
+        response = self.client.get(reverse("shop_portal:sales"))
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(response, "Dragon")
+        self.assertContains(response, "Fox")
+        self.assertContains(response, "114.00")
+        self.assertContains(response, "Orders per day")
+        self.assertContains(response, "Revenue per day")
+
+    def test_portal_nav_and_home_stats(self):
+        _sold_order(self.dragon, qty=1)
+        home = self.client.get(reverse("dashboard:home"))
+        self.assertEqual(home.status_code, 200)
+        self.assertEqual(home.context["shop_sales_30d"], 1)
+        self.assertEqual(home.context["shop_revenue_30d"], Decimal("18.00"))
+        self.assertContains(home, reverse("shop_portal:sales"))
+        self.assertContains(home, "Sales (30 days)")
+        products = self.client.get(reverse("shop_portal:product_list"))
+        self.assertContains(products, "Sales")
+        sales = self.client.get(reverse("shop_portal:sales"))
+        self.assertContains(sales, 'class="active"')
+