feat: Implement Slack, Trello, and Courier (ShipLogic) integration

- Add 14 domain events for order lifecycle (OrderCreated, OrderPacked, ShipmentCreated, ParcelDelivered, etc.)
- Create SlackNotifierService with channels for orders, design, production, shipping, ops-alerts
- Create TrelloService to create cards, move cards between lists, attach files, check items
- Create CourierService to integrate with ShipLogic API for shipment creation and document retrieval
- Create PackingController to explicitly capture packing dimensions and weight
- Create ShippingController with multi-layer guards: packing validation, payment/approval verification, idempotency
- Create TrelloWebhookController to handle incoming Trello webhooks as intent signals
- Create CourierWebhookController to handle Shiplogic status updates
- Create event listeners for Slack notifications and Trello card updates
- Create EventServiceProvider to register all events and listeners
- Add database migration for packing, courier, and Trello data columns
- Create config files for slack, trello, and courier integration
- Update .env with integration secrets placeholders
- Add routes for /orders/{id}/pack, /orders/{id}/ship, /api/webhooks/trello, /api/webhooks/courier

Key architectural decisions:
- Packing is explicit ops action (not automatic from status)
- Shipment creation only after: Trello intent + packing confirmed + payment/approval rules met
- Courier API failures keep order in Ready to Ship state (safe retry)
- Trello and Slack are mirrors of backend state, not decision makers
- All side effects flow through event listeners, maintaining separation of concerns

app/Events/DepositPaid.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace App\Events;
+
+use App\Models\Order;
+use Illuminate\Foundation\Events\Dispatchable;
+use Illuminate\Queue\SerializesModels;
+
+class DepositPaid
+{
+    use Dispatchable, SerializesModels;
+
+    public function __construct(
+        public Order $order,
+        public float $depositAmount,
+    ) {
+    }
+}