Add shop, POS sync, event ticketing, and shipping catalog apps (#6)

## Summary
- Closes #5
- Optional `shop`, `pos_sync`, `events`, and `shipping` apps gated by `FEATURE_*` flags
- Deps match the catalog: shop/events need email + Stripe; POS/shipping need shop
- Portal inventory, POS webhooks, capacity tickets, EasyPost/Pirate Ship shipping

## Test plan
- [ ] `manage.py test` (152 passed locally)
- [ ] Shop cart + paid order decrements stocked inventory
- [ ] POS inbound webhook decrements SKU; paid order queues outbound reserve
- [ ] Event capacity blocks overbook; paid order emails ticket codes
- [ ] Shipping stub label + Pirate Ship CSV of unshipped paid orders
- [ ] `validate-env.sh` rejects shop without email/payments, POS/shipping without shop

Reviewed-on: #6

site/dashboard/templates/dashboard/home.html

@@ -27,6 +27,36 @@
     <div class="value">{{ open_invoices|default:0 }}</div>
   </div>
   {% endif %}
+  {% if 'shop' in enabled_features %}
+  <div class="stat-card">
+    <div class="label">Open shop orders</div>
+    <div class="value">{{ open_shop_orders|default:0 }}</div>
+  </div>
+  <div class="stat-card">
+    <div class="label">Sales (30 days)</div>
+    <div class="value">{{ shop_sales_30d|default:0 }}</div>
+  </div>
+  <div class="stat-card">
+    <div class="label">Shop revenue (30 days)</div>
+    <div class="value" style="font-size:22px">{{ shop_revenue_30d|default:0 }}</div>
+  </div>
+  <div class="stat-card">
+    <div class="label">Low stock</div>
+    <div class="value">{{ low_stock_products|default:0 }}</div>
+  </div>
+  {% endif %}
+  {% if 'events' in enabled_features %}
+  <div class="stat-card">
+    <div class="label">Upcoming events</div>
+    <div class="value">{{ upcoming_events|default:0 }}</div>
+  </div>
+  {% endif %}
+  {% if 'shipping' in enabled_features %}
+  <div class="stat-card">
+    <div class="label">Unshipped orders</div>
+    <div class="value">{{ unshipped_orders|default:0 }}</div>
+  </div>
+  {% endif %}
 </div>
 
 <div class="split">