agent: unify listening and dialing with directed mutual measurements

Replace Probe with Agent across node runtime, Fleet contracts, backend state, API and storage. Report incoming sessions and outgoing link health through each Agent uplink, and retain directed link controls and retry.

Update protocol fixtures and end-to-end coverage for the unified model; accept requested cancellation during the Fleet timeout test cleanup.

backend/src/MoShiro.Backend.Application/Query/RowLoader.cs

@@ -130,7 +130,7 @@ public sealed class RowLoader
         {
             foreach (LineKey line in lines)
             {
-                Result<IReadOnlyList<SourceRow>> one = await LoadAsync(plan, range, line.Agent, line.Series, ct);
+                Result<IReadOnlyList<SourceRow>> one = await LoadAsync(plan, range, line.Listener, line.Series, ct);
                 if (!one.TryGet(out IReadOnlyList<SourceRow>? rows, out FleetError? error))
                 {
                     return Result<Dictionary<LineKey, IReadOnlyList<SourceRow>>>.Fail(error);
@@ -142,14 +142,14 @@ public sealed class RowLoader
             return Result<Dictionary<LineKey, IReadOnlyList<SourceRow>>>.Ok(result);
         }
 
-        // 每个 Probe 一个序列：按序列分组，每组一次查询
+        // 每个拨号方一个序列：按序列分组，每组一次查询
         foreach (IGrouping<string, LineKey> bySeries in lines.GroupBy(l => l.Series))
         {
-            NodeId[] agents = [.. bySeries.Select(l => l.Agent).Distinct()];
+            NodeId[] agents = [.. bySeries.Select(l => l.Listener).Distinct()];
             IReadOnlyList<MetricRow> all = await _metrics.ReadAgentsAsync(ToLevel(plan.Source), agents, bySeries.Key, range.FromMs, range.ToMs, ct);
             foreach (IGrouping<NodeId, MetricRow> group in all.GroupBy(r => r.AgentId))
             {
-                LineKey key = bySeries.First(l => l.Agent == group.Key);
+                LineKey key = bySeries.First(l => l.Listener == group.Key);
                 result[key] = Decode([.. group]);
             }
         }