CUB-53: add SignalR hub registration and configuration

backend/.gitignore

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+## .NET
+bin/
+obj/
+*.user
+*.suo
+*.cache
+*.dll
+*.pdb
+
+## IDE
+.vs/
+.idea/
+*.swp
+*~
+
+## OS
+.DS_Store
+Thumbs.db
+
+## Environment
+.env

backend/ControlCenter.Api.csproj

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+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="9.0.14" />
+  </ItemGroup>
+
+</Project>

backend/Hubs/AgentStatusHub.cs

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+using Microsoft.AspNetCore.SignalR;
+
+namespace ControlCenter.Api.Hubs;
+
+/// <summary>
+/// SignalR hub for broadcasting agent status updates to connected clients.
+///
+/// <para>
+/// Clients connect to this hub at the <c>/hub</c> endpoint to receive
+/// real-time agent state changes. A background service subscribes to
+/// OpenClaw Gateway events and pushes them through this hub.
+/// </para>
+///
+/// <para>
+/// Architecture note: This hub bridges OpenClaw Gateway events to SignalR clients.
+/// The full typed client interface and extension methods will be added in a
+/// subsequent task (CUB-55).
+/// </para>
+/// </summary>
+public class AgentStatusHub : Hub
+{
+    private readonly ILogger<AgentStatusHub> _logger;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AgentStatusHub"/> class.
+    /// </summary>
+    /// <param name="logger">Logger for diagnostic output.</param>
+    public AgentStatusHub(ILogger<AgentStatusHub> logger)
+    {
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// Overrides <see cref="Hub.OnConnectedAsync"/> to log new connections.
+    /// </summary>
+    public override Task OnConnectedAsync()
+    {
+        _logger.LogDebug("Client connected: {ConnectionId}", Context.ConnectionId);
+        return base.OnConnectedAsync();
+    }
+
+    /// <summary>
+    /// Overrides <see cref="Hub.OnDisconnectedAsync"/> to log disconnections.
+    /// SignalR automatically removes disconnected connections from all groups.
+    /// </summary>
+    /// <param name="exception">Exception that caused the disconnection, if any.</param>
+    public override Task OnDisconnectedAsync(Exception? exception)
+    {
+        _logger.LogDebug("Client disconnected: {ConnectionId}", Context.ConnectionId);
+        return base.OnDisconnectedAsync(exception);
+    }
+}

backend/Program.cs

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+using ControlCenter.Api.Hubs;
+
+var builder = WebApplication.CreateBuilder(args);
+
+// Add services to the container.
+builder.Services.AddOpenApi();
+
+// Register SignalR for real-time agent status updates
+builder.Services.AddSignalR();
+
+var app = builder.Build();
+
+// Configure the HTTP request pipeline.
+if (app.Environment.IsDevelopment())
+{
+    app.MapOpenApi();
+}
+
+app.UseHttpsRedirection();
+
+// Map SignalR hub endpoint
+app.MapHub<AgentStatusHub>("/hub");
+
+app.Run();

backend/Properties/launchSettings.json

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+{
+  "$schema": "https://json.schemastore.org/launchsettings.json",
+  "profiles": {
+    "http": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": false,
+      "applicationUrl": "http://localhost:5178",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    },
+    "https": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": false,
+      "applicationUrl": "https://localhost:7041;http://localhost:5178",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    }
+  }
+}

backend/appsettings.Development.json

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+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  }
+}

backend/appsettings.json

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+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  },
+  "AllowedHosts": "*"
+}