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/index.php

@@ -0,0 +1,43 @@
+<?php
+
+require_once __DIR__ . '/../vendor/autoload.php';
+
+use DistributingCarriers\Infrastructure\CommandBus;
+use DistributingCarriers\Infrastructure\Router;
+use DistributingCarriers\Infrastructure\CassandraEventStore;
+use DistributingCarriers\Application\Commands\RegisterCarrierCommand;
+use DistributingCarriers\Application\Handlers\RegisterCarrierHandler;
+
+// Initialize Infrastructure
+// Note: In a real app, you'd configure the Cassandra session here.
+// For this demo, we'll mock it or assume it's passed in.
+// Since we don't have a running Cassandra instance we can connect to easily without extension,
+// we will assume the $session is created.
+// $cluster = Cassandra::cluster()->build();
+// $session = $cluster->connect('distributing_carriers');
+
+// Mocking session for demonstration if extension is missing, or just placeholder.
+$session = null; // Placeholder
+
+$eventStore = new CassandraEventStore($session);
+$commandBus = new CommandBus();
+
+// Register Handlers
+$commandBus->register(RegisterCarrierCommand::class, new RegisterCarrierHandler($eventStore));
+
+// Router
+$router = new Router();
+
+$router->add('POST', '/register-carrier', function () use ($commandBus) {
+    // In a real app, parse body.
+    // For demo, we'll just create a dummy command.
+    $command = new RegisterCarrierCommand("Test Carrier", "test@example.com");
+    $commandBus->dispatch($command);
+});
+
+
+$method = $_SERVER['REQUEST_METHOD'] ?? 'GET';
+$uri = $_SERVER['REQUEST_URI'] ?? '/';
+
+
+$router->dispatch($method, $uri);