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/Hubs/IAgentStatusClient.cs

@@ -0,0 +1,30 @@
+namespace ControlCenter.Hubs;
+
+/// <summary>
+/// Strongly-typed client interface for the AgentStatus SignalR hub.
+/// Defines the methods the server can invoke on connected clients
+/// to push real-time agent status and task progress updates.
+/// 
+/// <para>All server-to-client calls go through this interface for
+/// compile-time safety — matching the pattern used by the
+/// Extrudex PrinterHub.</para>
+/// </summary>
+public interface IAgentStatusClient
+{
+    /// <summary>
+    /// Pushes an agent status change to all subscribed clients.
+    /// Fired whenever an agent's operational status changes
+    /// (e.g., idle → active, active → thinking, active → error).
+    /// </summary>
+    /// <param name="update">The full status update payload.</param>
+    /// <returns>A Task that completes when the client has processed the update.</returns>
+    Task AgentStatusChanged(AgentStatusUpdate update);
+
+    /// <summary>
+    /// Pushes a task progress update to all subscribed clients.
+    /// Fired when an agent reports progress on its current task.
+    /// </summary>
+    /// <param name="progress">The task progress update payload.</param>
+    /// <returns>A Task that completes when the client has processed the update.</returns>
+    Task AgentTaskProgress(TaskProgressUpdate progress);
+}