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

backend/Dtos/AgentStatusUpdateDto.cs

@@ -0,0 +1,75 @@
+namespace ControlCenter.Api.Dtos;
+
+/// <summary>
+/// Data transfer object for broadcasting agent status updates
+/// to all connected SignalR clients.
+/// </summary>
+public class AgentStatusUpdateDto
+{
+    /// <summary>
+    /// Agent identifier, e.g. "otto", "dex", "rex".
+    /// Not null — every update must identify the agent it refers to.
+    /// </summary>
+    public string AgentId { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Human-readable display name, e.g. "Otto", "Dex".
+    /// Not null — used by clients to render agent cards.
+    /// </summary>
+    public string DisplayName { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Role description, e.g. "Orchestrator Agent", "Backend Specialist".
+    /// Not null — provides context for the agent's function.
+    /// </summary>
+    public string Role { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Current operational status of the agent.
+    /// Maps to <see cref="Entities.AgentStatus"/> values as lowercase strings:
+    /// "active", "idle", "thinking", "error".
+    /// </summary>
+    public string Status { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Description of the agent's current task, if any.
+    /// Null when the agent is idle with no active task.
+    /// </summary>
+    public string? CurrentTask { get; set; }
+
+    /// <summary>
+    /// Task progress percentage (0–100).
+    /// Null when progress is not trackable for the current task.
+    /// </summary>
+    public int? TaskProgress { get; set; }
+
+    /// <summary>
+    /// Elapsed time string for the current task, e.g. "04m 12s".
+    /// Null when no task is active.
+    /// </summary>
+    public string? TaskElapsed { get; set; }
+
+    /// <summary>
+    /// Full session key, e.g. "agent:otto:telegram:direct:8787451565".
+    /// Not null — uniquely identifies the agent session.
+    /// </summary>
+    public string SessionKey { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Communication channel the agent is operating on, e.g. "telegram", "discord", "slack".
+    /// Not null — every agent session operates on exactly one channel.
+    /// </summary>
+    public string Channel { get; set; } = string.Empty;
+
+    /// <summary>
+    /// ISO 8601 timestamp of the agent's last activity.
+    /// Not null — used by clients to detect stale connections.
+    /// </summary>
+    public string LastActivity { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Error message when the agent status is "error".
+    /// Null when the agent is not in an error state.
+    /// </summary>
+    public string? ErrorMessage { get; set; }
+}