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/stats.py

@@ -0,0 +1,166 @@
+"""Sales dashboard aggregates for FEATURE_SHOP."""
+
+from __future__ import annotations
+
+from datetime import date, datetime, time, timedelta
+from decimal import Decimal
+
+from django.conf import settings
+from django.db.models import Count, F, Max, Q, Sum
+from django.utils import timezone
+
+from shop.models import Order, OrderItem
+
+SOLD_STATUSES = (Order.Status.PAID, Order.Status.FULFILLED)
+SALES_WINDOW_DAYS = 30
+
+
+def _money(value) -> Decimal:
+    return (value or Decimal("0")).quantize(Decimal("0.01"))
+
+
+def _window_start(days: int):
+    today = timezone.localdate()
+    start_date = today - timedelta(days=days - 1)
+    start_dt = timezone.make_aware(
+        datetime.combine(start_date, time.min),
+        timezone.get_current_timezone(),
+    )
+    return today, start_date, start_dt
+
+
+def _sold_orders(start_dt=None):
+    qs = Order.objects.filter(status__in=SOLD_STATUSES)
+    if start_dt is None:
+        return qs
+    return qs.filter(
+        Q(paid_at__gte=start_dt) | Q(paid_at__isnull=True, created_at__gte=start_dt)
+    )
+
+
+def _sale_date(order) -> date:
+    when = order.paid_at or order.created_at
+    return timezone.localtime(when).date()
+
+
+def _bar_pct(value: Decimal | int | float, peak: Decimal | int | float) -> int:
+    if not peak:
+        return 0
+    if not value:
+        return 0
+    return max(8, int(round((float(value) / float(peak)) * 100)))
+
+
+def sales_summary(*, days: int = SALES_WINDOW_DAYS) -> dict:
+    """Order count and revenue for the rolling sales window."""
+    _, _, start_dt = _window_start(days)
+    totals = _sold_orders(start_dt).aggregate(
+        order_count=Count("id"), revenue=Sum("amount")
+    )
+    return {
+        "order_count": int(totals["order_count"] or 0),
+        "revenue": _money(totals["revenue"]),
+    }
+
+
+def sales_dashboard(*, days: int = SALES_WINDOW_DAYS) -> dict:
+    """Paid/fulfilled order stats, daily series, and top products."""
+    _, start_date, start_dt = _window_start(days)
+    sold = _sold_orders(start_dt)
+    totals = sold.aggregate(order_count=Count("id"), revenue=Sum("amount"))
+    order_count = int(totals["order_count"] or 0)
+    revenue = _money(totals["revenue"])
+    units = int(
+        OrderItem.objects.filter(order__in=sold).aggregate(total=Sum("quantity"))[
+            "total"
+        ]
+        or 0
+    )
+    aov = _money(revenue / order_count) if order_count else Decimal("0.00")
+    currency = (settings.STRIPE_CURRENCY or "usd").lower()
+
+    by_day: dict = {
+        start_date + timedelta(days=offset): {
+            "count": 0,
+            "revenue": Decimal("0.00"),
+        }
+        for offset in range(days)
+    }
+    for order in sold.only("paid_at", "created_at", "amount"):
+        day = _sale_date(order)
+        bucket = by_day.get(day)
+        if bucket is None:
+            continue
+        bucket["count"] += 1
+        bucket["revenue"] += order.amount or Decimal("0")
+
+    peak_count = max((row["count"] for row in by_day.values()), default=0)
+    peak_revenue = max((row["revenue"] for row in by_day.values()), default=Decimal("0"))
+    daily_sales = []
+    daily_revenue = []
+    for index, (day, row) in enumerate(by_day.items()):
+        tick = index == 0 or index == days - 1 or day.weekday() == 0
+        label = f"{day.strftime('%b')} {day.day}"
+        daily_sales.append(
+            {
+                "date": day,
+                "label": label,
+                "count": row["count"],
+                "revenue": _money(row["revenue"]),
+                "pct": _bar_pct(row["count"], peak_count),
+                "tick": tick,
+                "tick_label": label if tick else "",
+            }
+        )
+        daily_revenue.append(
+            {
+                "date": day,
+                "label": label,
+                "count": row["count"],
+                "revenue": _money(row["revenue"]),
+                "pct": _bar_pct(row["revenue"], peak_revenue),
+                "tick": tick,
+                "tick_label": label if tick else "",
+            }
+        )
+
+    product_rows = list(
+        OrderItem.objects.filter(order__in=sold)
+        .values("sku")
+        .annotate(
+            units=Sum("quantity"),
+            revenue=Sum(F("unit_price") * F("quantity")),
+            product_name=Max("product__name"),
+            item_name=Max("name"),
+        )
+        .order_by("-units", "-revenue")[:8]
+    )
+    peak_units = max((int(row["units"] or 0) for row in product_rows), default=0)
+    top_products = []
+    for row in product_rows:
+        units_sold = int(row["units"] or 0)
+        top_products.append(
+            {
+                "sku": row["sku"],
+                "name": row["product_name"] or row["item_name"] or row["sku"],
+                "units": units_sold,
+                "revenue": _money(row["revenue"]),
+                "bar_pct": _bar_pct(units_sold, peak_units),
+            }
+        )
+
+    recent_orders = list(sold.order_by("-paid_at", "-created_at")[:8])
+
+    return {
+        "days": days,
+        "currency": currency,
+        "order_count": order_count,
+        "revenue": revenue,
+        "units_sold": units,
+        "aov": aov,
+        "daily_sales": daily_sales,
+        "daily_revenue": daily_revenue,
+        "top_products": top_products,
+        "recent_orders": recent_orders,
+        "has_sales": order_count > 0,
+    }