feat(ops): upload node logs and task traffic [CI]

backend/fleet/src/Fleet.Core/NodeSupport.cs

@@ -15,6 +15,17 @@ public interface INodeLog
     void Write(NodeLogLevel level, string message, params (string Key, object? Value)[] fields);
 }
 
+/// <summary>One structured node log line queued for delivery to the control plane.</summary>
+public sealed record NodeLogRecord(long AtUtcMs, string Level, string Message, Dictionary<string, string> Fields);
+
+public sealed record NodeLogBatch(IReadOnlyList<NodeLogRecord> Records, long Dropped);
+
+/// <summary>Optional bounded log source used by node heartbeats to upload recent local logs.</summary>
+public interface INodeLogBatchSource
+{
+    NodeLogBatch TakeBatch(int maxRecords);
+}
+
 public sealed class NullNodeLog : INodeLog
 {
     public static NullNodeLog Instance { get; } = new();