feat(core): Implement DDD, CQRS, and Event Sourcing architecture

- Add project README and Composer configuration with PSR-4 autoloading
- Implement domain layer with AggregateRoot base class for event sourcing
- Create Carrier aggregate with CarrierRegistered domain event
- Add application layer with RegisterCarrierCommand and RegisterCarrierHandler
- Implement infrastructure layer with EventStore interface and CassandraEventStore
- Add CommandBus and Router for request handling and routing
- Create demo test file to showcase carrier registration workflow
- Establish foundation for event-driven architecture with Cassandra persistence

src/Infrastructure/Router.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace DistributingCarriers\Infrastructure;
+
+class Router
+{
+    private $routes = [];
+
+    public function add(string $method, string $path, callable $handler): void
+    {
+        $this->routes[] = [
+            'method' => $method,
+            'path' => $path,
+            'handler' => $handler
+        ];
+    }
+
+    public function dispatch(string $method, string $uri)
+    {
+        foreach ($this->routes as $route) {
+            if ($route['method'] === $method && $route['path'] === $uri) {
+                return call_user_func($route['handler']);
+            }
+        }
+
+        http_response_code(404);
+        echo "Not Found";
+    }
+}