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.

Api/Program.cs

@@ -1,9 +1,13 @@
+using Api.SignalR;
+
 var builder = WebApplication.CreateBuilder(args);
 
 // Add services to the container.
 // Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi
 builder.Services.AddEndpointsApiExplorer();
 builder.Services.AddOpenApi();
+builder.Services.AddSignalR();
+builder.Services.AddHostedService<SignalRSendService>();
 builder.Services.AddOpenApiDocument(config =>
 {
     config.Title = "NSwag Demo API";
@@ -12,9 +16,10 @@ builder.Services.AddCors(options =>
 {
     options.AddDefaultPolicy(policy =>
     {
-        policy.AllowAnyOrigin()
+        policy.WithOrigins("http://localhost:3000") // Specify the allowed origin
               .AllowAnyHeader()
-              .AllowAnyMethod();
+              .AllowAnyMethod()
+              .AllowCredentials(); // Allow credentials
     });
 });
 
@@ -36,7 +41,7 @@ var summaries = new[]
     "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
 };
 
-app.MapGet("/weatherforecast", () =>
+app.MapGet("/weatherforecast", async () =>
 {
     var forecast =  Enumerable.Range(1, 5).Select(index =>
         new WeatherForecast
@@ -46,10 +51,15 @@ app.MapGet("/weatherforecast", () =>
             summaries[Random.Shared.Next(summaries.Length)]
         ))
         .ToArray();
+
     return forecast;
 })
 .WithName("GetWeatherForecast");
 
+
+// Add SignalR hub
+app.MapHub<WeatherUpdateHub>("/WeatherUpdateHub");
+
 app.Run();
 
 record WeatherForecast(DateOnly Date, int TemperatureC, string? Summary)