Add SignalR integration for real-time weather updates

Implemented SignalR to enable real-time communication between the server and connected clients. Added a new hub (`WeatherUpdateHub`), a background service (`SignalRSendService`), and modified both the API backend and React frontend for seamless message broadcasting and handling.

react-client/package.json

@@ -3,6 +3,7 @@
   "version": "0.1.0",
   "private": true,
   "dependencies": {
+    "@microsoft/signalr": "^8.0.7",
     "@testing-library/jest-dom": "^5.14.1",
     "@testing-library/react": "^13.0.0",
     "@testing-library/user-event": "^13.2.1",