feat: wire consumer pause/resume API endpoint (Gap 7.5)

Enhances HandlePause to parse pause_until (RFC3339) for time-bounded
pauses and returns current pause state in the response body. Adds
Paused/PauseUntil properties and PauseResponse factory to
JetStreamApiResponse. Covers 10 new parity tests.

src/NATS.Server/JetStream/Api/Handlers/ConsumerApiHandlers.cs

@@ -84,10 +84,23 @@ public static class ConsumerApiHandlers
             return JetStreamApiResponse.NotFound(subject);
 
         var (stream, durableName) = parsed.Value;
-        var paused = ParsePause(payload);
-        return consumerManager.Pause(stream, durableName, paused)
-            ? JetStreamApiResponse.SuccessResponse()
-            : JetStreamApiResponse.NotFound(subject);
+
+        var (paused, pauseUntil) = ParsePauseRequest(payload);
+
+        bool success;
+        if (pauseUntil.HasValue)
+            success = consumerManager.Pause(stream, durableName, pauseUntil.Value);
+        else if (paused)
+            success = consumerManager.Pause(stream, durableName, true);
+        else
+            success = consumerManager.Resume(stream, durableName);
+
+        if (!success)
+            return JetStreamApiResponse.NotFound(subject);
+
+        return JetStreamApiResponse.PauseResponse(
+            consumerManager.IsPaused(stream, durableName),
+            consumerManager.GetPauseUntil(stream, durableName));
     }
 
     public static JetStreamApiResponse HandleReset(string subject, ConsumerManager consumerManager)
@@ -359,22 +372,44 @@ public static class ConsumerApiHandlers
         return 1;
     }
 
-    private static bool ParsePause(ReadOnlySpan<byte> payload)
+    /// <summary>
+    /// Parses pause request payload supporting both a boolean <c>pause</c> field and an RFC3339
+    /// <c>pause_until</c> deadline. When <c>pause_until</c> is present it implies <c>pause=true</c>.
+    /// Go reference: server/consumer.go jsConsumerPauseRequest.
+    /// </summary>
+    private static (bool Paused, DateTime? PauseUntil) ParsePauseRequest(ReadOnlySpan<byte> payload)
     {
         if (payload.IsEmpty)
-            return false;
+            return (false, null);
 
         try
         {
             using var doc = JsonDocument.Parse(payload.ToArray());
-            if (doc.RootElement.TryGetProperty("pause", out var pauseEl))
-                return pauseEl.ValueKind == JsonValueKind.True;
+            var root = doc.RootElement;
+
+            DateTime? pauseUntil = null;
+            if (root.TryGetProperty("pause_until", out var untilEl)
+                && untilEl.ValueKind == JsonValueKind.String
+                && DateTime.TryParse(untilEl.GetString(), null, System.Globalization.DateTimeStyles.RoundtripKind, out var dt))
+            {
+                pauseUntil = dt.ToUniversalTime();
+            }
+
+            bool paused = false;
+            if (root.TryGetProperty("pause", out var pauseEl))
+                paused = pauseEl.ValueKind == JsonValueKind.True;
+
+            // pause_until implies pause=true (Go reference: consumer.go pauseConsumer).
+            if (pauseUntil.HasValue)
+                paused = true;
+
+            return (paused, pauseUntil);
         }
         catch (JsonException)
         {
         }
 
-        return false;
+        return (false, null);
     }
 
     private static string? ParseStreamSubject(string subject, string prefix)

src/NATS.Server/JetStream/Api/JetStreamApiResponse.cs

@@ -17,6 +17,18 @@ public sealed class JetStreamApiResponse
     public bool Success { get; init; }
     public ulong Purged { get; init; }
 
+    /// <summary>
+    /// Whether the consumer is currently paused. Populated by pause/resume API responses.
+    /// Go reference: server/consumer.go jsConsumerPauseResponse.paused field.
+    /// </summary>
+    public bool? Paused { get; init; }
+
+    /// <summary>
+    /// UTC deadline until which the consumer is paused. Null when no deadline is set.
+    /// Go reference: server/consumer.go jsConsumerPauseResponse.pause_until field.
+    /// </summary>
+    public DateTime? PauseUntil { get; init; }
+
     public static JetStreamApiResponse NotFound(string subject) => new()
     {
         Error = new JetStreamApiError
@@ -66,6 +78,17 @@ public sealed class JetStreamApiResponse
         Success = true,
         Purged = purged,
     };
+
+    /// <summary>
+    /// Returns a pause/resume success response with current pause state.
+    /// Go reference: server/consumer.go jsConsumerPauseResponse — returned after pause/resume API call.
+    /// </summary>
+    public static JetStreamApiResponse PauseResponse(bool paused, DateTime? pauseUntil) => new()
+    {
+        Success = true,
+        Paused = paused,
+        PauseUntil = pauseUntil,
+    };
 }
 
 public sealed class JetStreamStreamInfo
@@ -102,6 +125,15 @@ public sealed class JetStreamDirectMessage
 public sealed class JetStreamSnapshot
 {
     public string Payload { get; init; } = string.Empty;
+
+    /// <summary>Stream name this snapshot was taken from.</summary>
+    public string? StreamName { get; init; }
+
+    /// <summary>Number of chunks the snapshot was split into (1 for non-chunked snapshots).</summary>
+    public int NumChunks { get; init; }
+
+    /// <summary>Block/chunk size in bytes.</summary>
+    public int BlkSize { get; init; }
 }
 
 public sealed class JetStreamPullBatch