feat: add multi-agent chat cockpit and context controls

AgentChat.cs

@@ -0,0 +1,23 @@
+sealed class AgentChatEntry
+{
+    public required string Id { get; init; }
+    public required DateTimeOffset Time { get; init; }
+    public required string Type { get; init; }
+    public string Text { get; set; } = string.Empty;
+    public string? Title { get; set; }
+    public string? Status { get; set; }
+    public string? ToolKind { get; set; }
+    public string? ToolCallId { get; set; }
+
+    public object Snapshot() => new
+    {
+        id = Id,
+        time = Time,
+        type = Type,
+        text = Text,
+        title = Title,
+        status = Status,
+        toolKind = ToolKind,
+        toolCallId = ToolCallId
+    };
+}