feat(CUB-55): add SignalR broadcast state method with AgentStatusHub and DTO

backend/Program.cs

@@ -1,4 +1,5 @@
 using ControlCenter.Api.Data;
+using ControlCenter.Api.Hubs;
 using Microsoft.EntityFrameworkCore;
 
 var builder = WebApplication.CreateBuilder(args);
@@ -6,6 +7,9 @@ var builder = WebApplication.CreateBuilder(args);
 // Add services to the container.
 builder.Services.AddOpenApi();
 
+// Register SignalR for real-time agent status updates
+builder.Services.AddSignalR();
+
 // Register DbContext with PostgreSQL
 builder.Services.AddDbContext<AppDbContext>(options =>
 {
@@ -28,4 +32,7 @@ if (app.Environment.IsDevelopment())
 
 app.UseHttpsRedirection();
 
+// Map SignalR hubs
+app.MapHub<AgentStatusHub>("/hubs/agent-status");
+
 app.Run();