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/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