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

scripts/validate-env.sh

@@ -128,7 +128,7 @@ done
 if ((${#missing[@]} > 0)); then
   echo "Missing required environment variables in $ENV_FILE:" >&2
   printf '  - %s\n' "${missing[@]}" >&2
-  echo "Copy .env.prod.example to ~/Documents/secrets/<slug>_site/<slug>_site_${DJANGO_ENV}.env and set values." >&2
+  echo "Copy .env.prod.example to ~/Documents/secrets/print_forge/print_forge_${DJANGO_ENV}.env and set values." >&2
   exit 1
 fi