feat(CUB-56): Agent State Database Migration

backend/Entities/Agent.cs

@@ -0,0 +1,59 @@
+namespace ControlCenter.Api.Entities;
+
+/// <summary>
+/// Represents an agent's current state in the Control Center.
+/// Each row tracks one agent session's status, task, and activity.
+/// </summary>
+public class Agent
+{
+    /// <summary>
+    /// Primary key — UUID generated on insert.
+    /// </summary>
+    public Guid Id { get; set; }
+
+    /// <summary>
+    /// Current operational status of the agent.
+    /// Stored as an enum in PostgreSQL via Npgsql.
+    /// </summary>
+    public AgentStatus Status { get; set; } = AgentStatus.Idle;
+
+    /// <summary>
+    /// Description of the agent's current task, if any.
+    /// Nullable — not all agents have an active task.
+    /// </summary>
+    public string? Task { get; set; }
+
+    /// <summary>
+    /// Task progress percentage (0–100).
+    /// Nullable — progress is only meaningful when an agent has a trackable task.
+    /// </summary>
+    public int? Progress { get; set; }
+
+    /// <summary>
+    /// Full session key, e.g. "agent:otto:telegram:direct:8787451565".
+    /// Not null — every agent row must be associated with a 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>
+    /// Timestamp of the agent's last activity.
+    /// Default: current UTC timestamp on insert.
+    /// </summary>
+    public DateTime LastActivity { get; set; } = DateTime.UtcNow;
+
+    /// <summary>
+    /// Row creation timestamp. Set automatically on insert.
+    /// </summary>
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    /// <summary>
+    /// Row last-update timestamp. Updated automatically on any modification.
+    /// </summary>
+    public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+}

backend/Entities/AgentStatus.cs

@@ -0,0 +1,13 @@
+namespace ControlCenter.Api.Entities;
+
+/// <summary>
+/// Agent operational status enum.
+/// Maps to the agent_status enum type in PostgreSQL.
+/// </summary>
+public enum AgentStatus
+{
+    Active = 0,
+    Idle = 1,
+    Thinking = 2,
+    Error = 3
+}