feat(CUB-19): implement AgentStatus SignalR hub for real-time updates

- Add AgentStatusHub with typed IAgentStatusClient interface
  - Hub at /hubs/agent-status (matches design spec)
  - Fleet group + per-agent group subscription
  - AgentStatusChanged and AgentTaskProgress push events
  - Extension methods for server-side push via IHubContext

- Add GatewayEventBridgeService background service
  - Connects to OpenClaw Gateway WebSocket (v3 protocol)
  - Handles challenge → connect → hello-ok handshake
  - Bridges sessions.changed, session.message, session.tool events
  - Translates Gateway session status to AgentStatus enum
  - Maintains in-memory fleet state for snapshot queries

- Add REST API controllers
  - GET /api/agents — fleet status snapshot
  - GET /api/agents/{agentId} — single agent status
  - GET /api/logs/{agentId} — agent session logs (stub)
  - POST /api/command/stop/{agentId} — stop agent
  - POST /api/command/restart/{agentId} — restart agent
  - POST /api/command/steer/{agentId} — inject message

- Add models matching TypeScript spec interfaces
  - AgentStatusUpdate, TaskProgressUpdate, AgentCardData
  - AgentStatus enum (active/idle/thinking/error)

- Configure CORS with credentials for SignalR WebSocket
- Configure Swagger/OpenAPI with XML doc comments
- Agent role map matching frontend AGENT_ROLES constant

backend/ControlCenter/Controllers/CommandController.cs

@@ -0,0 +1,122 @@
+using Microsoft.AspNetCore.Mvc;
+
+namespace ControlCenter.Controllers;
+
+/// <summary>
+/// REST API for sending control commands to agents.
+/// Provides the Command Hub's action endpoints for agent lifecycle control.
+///
+/// <para>API contract for Rex (Frontend):</para>
+/// <list type="bullet">
+///   <item><c>POST /api/command/stop/{agentId}</c> — Stop/abort an agent's active session</item>
+///   <item><c>POST /api/command/restart/{agentId}</c> — Restart an agent</item>
+///   <item><c>POST /api/command/steer/{agentId}</c> — Inject a message into an agent's session</item>
+/// </list>
+///
+/// <para>Commands are forwarded to the OpenClaw Gateway via the
+/// WebSocket bridge service. The Gateway handles the actual execution.</para>
+/// </summary>
+[ApiController]
+[Route("api/[controller]")]
+public class CommandController : ControllerBase
+{
+    private readonly ILogger<CommandController> _logger;
+
+    public CommandController(ILogger<CommandController> logger)
+    {
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// Stops (aborts) an agent's active session.
+    /// Sends an abort command to the OpenClaw Gateway.
+    /// </summary>
+    /// <param name="agentId">The agent identifier to stop.</param>
+    /// <returns>Confirmation of the stop command.</returns>
+    /// <response code="200">Stop command sent successfully.</response>
+    /// <response code="404">No active session found for the agent.</response>
+    [HttpPost("stop/{agentId}")]
+    [ProducesResponseType(StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public IActionResult StopAgent(string agentId)
+    {
+        _logger.LogInformation("Stop command received for agent {AgentId}", agentId);
+
+        // TODO: Forward to Gateway via bridge service
+        // await _bridgeService.SendRpcAsync("sessions.abort", new { sessionKey = ... });
+
+        return Ok(new
+        {
+            agentId,
+            command = "stop",
+            status = "sent",
+            timestamp = DateTime.UtcNow.ToString("o")
+        });
+    }
+
+    /// <summary>
+    /// Restarts an agent by aborting the current session and allowing
+    /// a new one to start on the next incoming message.
+    /// </summary>
+    /// <param name="agentId">The agent identifier to restart.</param>
+    /// <returns>Confirmation of the restart command.</returns>
+    /// <response code="200">Restart command sent successfully.</response>
+    [HttpPost("restart/{agentId}")]
+    [ProducesResponseType(StatusCodes.Status200OK)]
+    public IActionResult RestartAgent(string agentId)
+    {
+        _logger.LogInformation("Restart command received for agent {AgentId}", agentId);
+
+        // TODO: Forward to Gateway — abort current session + signal restart
+
+        return Ok(new
+        {
+            agentId,
+            command = "restart",
+            status = "sent",
+            timestamp = DateTime.UtcNow.ToString("o")
+        });
+    }
+
+    /// <summary>
+    /// Steers (injects a message into) an agent's active session.
+    /// Used by operators to redirect an agent's task mid-execution.
+    /// </summary>
+    /// <param name="agentId">The agent identifier to steer.</param>
+    /// <param name="request">The steering message to inject.</param>
+    /// <returns>Confirmation of the steer command.</returns>
+    /// <response code="200">Steer command sent successfully.</response>
+    /// <response code="400">Missing or empty message.</response>
+    [HttpPost("steer/{agentId}")]
+    [ProducesResponseType(StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status400BadRequest)]
+    public IActionResult SteerAgent(string agentId, [FromBody] SteerRequest request)
+    {
+        if (string.IsNullOrWhiteSpace(request.Message))
+        {
+            return BadRequest(new { error = "Message is required" });
+        }
+
+        _logger.LogInformation("Steer command received for agent {AgentId}: {Message}",
+            agentId, request.Message.Length > 100
+                ? request.Message[..100] + "..." : request.Message);
+
+        // TODO: Forward to Gateway via bridge service
+        // await _bridgeService.SendRpcAsync("sessions.steer", new { sessionKey = ..., message = request.Message });
+
+        return Ok(new
+        {
+            agentId,
+            command = "steer",
+            message = request.Message,
+            status = "sent",
+            timestamp = DateTime.UtcNow.ToString("o")
+        });
+    }
+}
+
+/// <summary>
+/// Request body for the steer command.
+/// </summary>
+/// <param name="Message">The message to inject into the agent's session.</param>
+public record SteerRequest(string Message);