fix(clients): render ReplayGap as the typed cross-CLI row in the .NET and Java CLIs (NEXT-02)

The .NET and Java stream-events commands handed the raw ReplayGap sentinel
MxEvent to their protobuf JSON formatters (Java text mode printed
'0 MX_EVENT_FAMILY_UNSPECIFIED'), while the Go/Python/Rust CLIs already emit
the typed row (CLI-35/36). Both now branch on the sentinel: Java text mode
prints 'REPLAY_GAP requested_after=<n> oldest_available=<n>' and JSON mode a
hand-built {"replayGap":{...}} line via nextItem()/isReplayGap(); the .NET
CLI emits the same hand-built row in jsonl/text (its text mode is
JSON-per-line) and inside the --json events array. Rows are hand-built so
the cursors are JSON numbers like the other three CLIs, not the proto3 JSON
mapping's quoted uint64 strings — the CrossLanguageSmokeMatrix divergence
table collapses to a single converged contract.

Tests: .NET MxGatewayClientCliTests 35/35 (new RendersReplayGapAsTypedRow
covers jsonl + aggregate); Java gradle test 52/52 (new
streamEventsRendersReplayGapAsTypedRow covers --json + text over the
in-process harness). No generated-file churn.

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Cli/MxGatewayClientCli.cs

@@ -1418,14 +1418,16 @@ public static class MxGatewayClientCli
                 .WithCancellation(cancellationToken)
                 .ConfigureAwait(false))
             {
-                if (jsonLines)
-                {
-                    output.WriteLine(ProtobufJsonFormatter.Format(gatewayEvent));
-                }
-                else if (json)
+                if (json && !jsonLines)
                 {
                     events.Add(gatewayEvent);
                 }
+                else if (gatewayEvent.ReplayGap is { } replayGap)
+                {
+                    // Render the ReplayGap sentinel as the typed cross-CLI row instead of the raw
+                    // sentinel MxEvent (NEXT-02, mirroring the Go/Python/Rust CLIs).
+                    output.WriteLine(FormatReplayGapRow(replayGap));
+                }
                 else
                 {
                     output.WriteLine(ProtobufJsonFormatter.Format(gatewayEvent));
@@ -1835,7 +1837,31 @@ public static class MxGatewayClientCli
 
     private static JsonElement EventToJsonElement(MxEvent gatewayEvent)
     {
-        return JsonDocument.Parse(ProtobufJsonFormatter.Format(gatewayEvent)).RootElement.Clone();
+        string row = gatewayEvent.ReplayGap is { } replayGap
+            ? FormatReplayGapRow(replayGap)
+            : ProtobufJsonFormatter.Format(gatewayEvent);
+        return JsonDocument.Parse(row).RootElement.Clone();
+    }
+
+    /// <summary>
+    ///     Formats the typed ReplayGap row shared by the CLIs (NEXT-02). Hand-built so the
+    ///     cursors are JSON numbers like the Go/Python/Rust rows, not the protobuf JSON
+    ///     formatter's quoted uint64 strings.
+    /// </summary>
+    /// <param name="replayGap">Replay gap sentinel payload.</param>
+    /// <returns>A single-line JSON row describing the gap.</returns>
+    private static string FormatReplayGapRow(ReplayGap replayGap)
+    {
+        return JsonSerializer.Serialize(
+            new
+            {
+                replayGap = new
+                {
+                    requestedAfterSequence = replayGap.RequestedAfterSequence,
+                    oldestAvailableSequence = replayGap.OldestAvailableSequence,
+                },
+            },
+            JsonOptions);
     }
 
     private static MxValue ParseValue(CliArguments arguments)