feat(historian): #675 reverse HistoryRead-Events paging + end-only backward reads

- IHistorianDataSource.ReadEventsAsync(..., bool reverse, ...) overload: reverse = Part 11 window (lo, hi]
  newest-first by (time, id) DESC. Default forwards forward reads and throws NotSupportedException for
  reverse (Null); Gateway refuses explicitly (ascending-only stream). Server answers
  BadHistoryOperationUnsupported instead of silently returning the earliest N ascending.
- SqlServer / QuestDB serve reverse natively (ORDER BY time DESC, id DESC + TOP/LIMIT).
- Node manager: reverse event reads page with continuation points; direction stored in the cursor
  (HistoryContinuationState.Reverse) so a resume continues in the cursor's direction; reverse tie clusters
  over-fetched forward and sliced from the newest end (SliceTieCluster(reverse:)); end-only reads with a
  cap page backward from EndTime (mirrors raw).
- Resumed event pages over-fetch by the boundary skip, so every non-final page is a full cap page.
- Tests: node-manager reverse paging (ties, clusters, coarse resolution, overfetch bound, resume
  direction both ways, end-only, unsupported backend); shared EventReadConformance on SqlServer +
  QuestDB; over-the-wire reverse paging; offline Gateway pin of the UTC DateTime.MaxValue bound through
  the published client's proto conversion (in-process gRPC capture) and FILETIME.
- docs/Historian.md event paging section.

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.SqlServer.IntegrationTests/SqlServerConformance.cs

@@ -60,3 +60,10 @@ public sealed class SqlServerModifiedValueConformance(SqlHistorianFixture fx) :
     /// <inheritdoc/>
     protected override Task<IConformanceBackend> CreateBackendAsync() => SqlServerConformanceBackend.CreateAsync(fx);
 }
+
+[Collection(SqlHistorianCollection.Name)]
+public sealed class SqlServerEventReadConformance(SqlHistorianFixture fx) : EventReadConformance
+{
+    /// <inheritdoc/>
+    protected override Task<IConformanceBackend> CreateBackendAsync() => SqlServerConformanceBackend.CreateAsync(fx);
+}

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.SqlServer.IntegrationTests/SqlServerConformanceBackend.cs

@@ -40,6 +40,22 @@ internal sealed class SqlServerConformanceBackend : IConformanceBackend
     public async Task SeedAsync(string tag, params (DateTime T, HistorianValue V, uint Status)[] samples) =>
         await _db.SeedAsync(tag, samples);
 
+    /// <inheritdoc/>
+    public async Task SeedEventsAsync(params (DateTime T, string Id, string Source)[] events)
+    {
+        await using var c = await _db.Conn.OpenAsync(CancellationToken.None);
+        foreach (var (t, id, source) in events)
+        {
+            await using var cmd = _db.Conn.CreateCommand(c,
+                $"INSERT {_db.Conn.Q("Event")} (EventId, SourceName, AlarmId, AlarmName, AlarmTypeName, Severity, EventKind, Message, " +
+                "UserName, Comment, EventTimeUtc, ReceivedTimeUtc) VALUES (@id, @src, 'a', 'n', 'T', 500, 'Activated', NULL, NULL, NULL, @t, @t)");
+            cmd.Parameters.AddWithValue("@id", id);
+            cmd.Parameters.AddWithValue("@src", source);
+            SqlHistorianConnection.AddDateTime2(cmd, "@t", t);
+            await cmd.ExecuteNonQueryAsync();
+        }
+    }
+
     /// <inheritdoc/>
     public async Task<IReadOnlyList<(DateTime T, HistorianValue V, uint Status)>> ReadBackAsync(string tag)
     {