chore: restructure project into backend and frontend folders

- Move all frontend code to frontend/ directory
- Add backend/ with Go project structure (cmd, internal, pkg)
- Add docker-compose.yml for orchestration

frontend/src/hooks/useWebSocket.ts

@@ -0,0 +1,83 @@
+import { useEffect, useCallback } from 'react';
+import { useDeliveryStore } from '../stores/deliveryStore';
+import type { Delivery } from '../types';
+
+type WebSocketEvent = 
+  | { type: 'delivery.created'; payload: Delivery }
+  | { type: 'delivery.updated'; payload: Delivery }
+  | { type: 'delivery.deleted'; payload: { id: string } };
+
+type EventHandler = (event: WebSocketEvent) => void;
+
+class MockWebSocket {
+  private handlers: EventHandler[] = [];
+  private isConnected = false;
+
+  connect() {
+    this.isConnected = true;
+    console.log('WebSocket connected (mock)');
+  }
+
+  disconnect() {
+    this.isConnected = false;
+    console.log('WebSocket disconnected (mock)');
+  }
+
+  subscribe(handler: EventHandler) {
+    this.handlers.push(handler);
+    return () => {
+      this.handlers = this.handlers.filter((h) => h !== handler);
+    };
+  }
+
+  emit(event: WebSocketEvent) {
+    if (!this.isConnected) return;
+    this.handlers.forEach((handler) => handler(event));
+  }
+
+  simulateIncomingEvent(event: WebSocketEvent) {
+    this.emit(event);
+  }
+}
+
+const mockWebSocket = new MockWebSocket();
+
+export const useWebSocket = () => {
+  const { addDelivery, updateDelivery, deleteDelivery } = useDeliveryStore();
+
+  useEffect(() => {
+    mockWebSocket.connect();
+
+    const unsubscribe = mockWebSocket.subscribe((event) => {
+      switch (event.type) {
+        case 'delivery.created':
+          addDelivery(event.payload);
+          break;
+        case 'delivery.updated':
+          updateDelivery(event.payload.id, event.payload);
+          break;
+        case 'delivery.deleted':
+          deleteDelivery(event.payload.id);
+          break;
+      }
+    });
+
+    return () => {
+      unsubscribe();
+      mockWebSocket.disconnect();
+    };
+  }, [addDelivery, updateDelivery, deleteDelivery]);
+
+  const sendEvent = useCallback((event: WebSocketEvent) => {
+    mockWebSocket.emit(event);
+  }, []);
+
+  return { sendEvent, isConnected: true };
+};
+
+export const simulateIncomingDelivery = (delivery: Delivery) => {
+  mockWebSocket.simulateIncomingEvent({
+    type: 'delivery.created',
+    payload: delivery,
+  });
+};