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/client_site/settings/base.py

@@ -115,11 +115,27 @@ FEATURE_BLOG = env_bool("FEATURE_BLOG", _feature_default)
 FEATURE_PAYMENTS = env_bool("FEATURE_PAYMENTS", _feature_default)
 FEATURE_SOCIAL = env_bool("FEATURE_SOCIAL", _feature_default)
 FEATURE_SOCIAL_AI = env_bool("FEATURE_SOCIAL_AI", _feature_default)
+FEATURE_SHOP = env_bool("FEATURE_SHOP", _feature_default)
+FEATURE_POS_SYNC = env_bool("FEATURE_POS_SYNC", _feature_default)
+FEATURE_EVENTS = env_bool("FEATURE_EVENTS", _feature_default)
+FEATURE_SHIPPING = env_bool("FEATURE_SHIPPING", _feature_default)
 
 if FEATURE_PAYMENTS and not FEATURE_EMAIL_SMS:
     raise ImproperlyConfigured("FEATURE_PAYMENTS requires FEATURE_EMAIL_SMS")
 if FEATURE_SOCIAL_AI and not FEATURE_SOCIAL:
     raise ImproperlyConfigured("FEATURE_SOCIAL_AI requires FEATURE_SOCIAL")
+if FEATURE_SHOP and not FEATURE_EMAIL_SMS:
+    raise ImproperlyConfigured("FEATURE_SHOP requires FEATURE_EMAIL_SMS")
+if FEATURE_SHOP and not FEATURE_PAYMENTS:
+    raise ImproperlyConfigured("FEATURE_SHOP requires FEATURE_PAYMENTS")
+if FEATURE_POS_SYNC and not FEATURE_SHOP:
+    raise ImproperlyConfigured("FEATURE_POS_SYNC requires FEATURE_SHOP")
+if FEATURE_EVENTS and not FEATURE_EMAIL_SMS:
+    raise ImproperlyConfigured("FEATURE_EVENTS requires FEATURE_EMAIL_SMS")
+if FEATURE_EVENTS and not FEATURE_PAYMENTS:
+    raise ImproperlyConfigured("FEATURE_EVENTS requires FEATURE_PAYMENTS")
+if FEATURE_SHIPPING and not FEATURE_SHOP:
+    raise ImproperlyConfigured("FEATURE_SHIPPING requires FEATURE_SHOP")
 
 CORE_APPS = [
     "core.apps.CoreConfig",
@@ -137,6 +153,10 @@ OPTIONAL_APPS = [
     (FEATURE_PAYMENTS, "payments.apps.PaymentsConfig"),
     (FEATURE_SOCIAL, "social.apps.SocialConfig"),
     (FEATURE_SOCIAL_AI, "social_ai.apps.SocialAiConfig"),
+    (FEATURE_SHOP, "shop.apps.ShopConfig"),
+    (FEATURE_POS_SYNC, "pos_sync.apps.PosSyncConfig"),
+    (FEATURE_EVENTS, "events.apps.EventsConfig"),
+    (FEATURE_SHIPPING, "shipping.apps.ShippingConfig"),
 ]
 DJANGO_APPS = [
     "django.contrib.admin",
@@ -352,6 +372,20 @@ STRIPE_PUBLISHABLE_KEY = env("STRIPE_PUBLISHABLE_KEY", "")
 STRIPE_WEBHOOK_SECRET = env("STRIPE_WEBHOOK_SECRET", "")
 STRIPE_CURRENCY = env("STRIPE_CURRENCY", "usd")
 
+# --- Shop / POS / shipping (FEATURE_SHOP and add-ons) ---
+# 0 = unlimited made-to-order print queue.
+SHOP_PRINT_QUEUE_LIMIT_MINUTES = int(
+    env("SHOP_PRINT_QUEUE_LIMIT_MINUTES", "0") or "0"
+)
+POS_WEBHOOK_SECRET = env("POS_WEBHOOK_SECRET", "")
+POS_API_BASE_URL = env("POS_API_BASE_URL", "")
+POS_API_TOKEN = env("POS_API_TOKEN", "")
+EASYPOST_API_KEY = env("EASYPOST_API_KEY", "")
+SHIP_FROM_LINE1 = env("SHIP_FROM_LINE1", "")
+SHIP_FROM_CITY = env("SHIP_FROM_CITY", "")
+SHIP_FROM_STATE = env("SHIP_FROM_STATE", "")
+SHIP_FROM_ZIP = env("SHIP_FROM_ZIP", "")
+
 # --- Nominatim (address suggest; server-side proxy only) ---
 # Self-hosted on ai-server-4080. Nominatim has no native API keys — gate with
 # LAN UFW + this Django proxy. Optional NOMINATIM_API_KEY is forwarded as