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.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.SqlServer/SqlServerHistorianDataSource.cs

@@ -314,8 +314,18 @@ public sealed class SqlServerHistorianDataSource : IHistorianDataSource
     ///     of <c>"{EventTimeUtc.Ticks}|{EventId}"</c> of that first not-returned event (opaque to callers; only
     ///     its presence is contractual).
     /// </remarks>
+    public Task<HistoricalEventsResult> ReadEventsAsync(
+        string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents, CancellationToken cancellationToken) =>
+        ReadEventsAsync(sourceName, startUtc, endUtc, maxEvents, reverse: false, cancellationToken);
+
+    /// <inheritdoc />
+    /// <remarks>
+    ///     Forward is the five-argument read. Reverse (Gitea #675) is <c>(lo, hi]</c> ordered by
+    ///     <c>(EventTimeUtc, EventId)</c> DESCENDING — the clustered index scanned backwards — so <c>TOP</c> keeps the latest
+    ///     events; truncation and the continuation point work as forward.
+    /// </remarks>
     public async Task<HistoricalEventsResult> ReadEventsAsync(
-        string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents, CancellationToken cancellationToken)
+        string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents, bool reverse, CancellationToken cancellationToken)
     {
         // No stored event can carry a source longer than the column (the alarm writer dead-letters it rather than
         // truncating), so an over-long filter matches nothing — never a truncated prefix of someone else's source.
@@ -328,9 +338,10 @@ public sealed class SqlServerHistorianDataSource : IHistorianDataSource
             var bounded = maxEvents > 0 && maxEvents < int.MaxValue;
             var sql =
                 $"SELECT {(bounded ? "TOP (@take) " : "")}EventId, SourceName, EventTimeUtc, ReceivedTimeUtc, Message, Severity " +
-                $"FROM {_conn.Q("Event")} WHERE EventTimeUtc >= @lo AND EventTimeUtc < @hi" +
+                $"FROM {_conn.Q("Event")} WHERE " +
+                (reverse ? "EventTimeUtc > @lo AND EventTimeUtc <= @hi" : "EventTimeUtc >= @lo AND EventTimeUtc < @hi") +
                 (sourceName is null ? "" : " AND SourceName = @source") +
-                " ORDER BY EventTimeUtc ASC, EventId ASC";
+                (reverse ? " ORDER BY EventTimeUtc DESC, EventId DESC" : " ORDER BY EventTimeUtc ASC, EventId ASC");
 
             await using var conn = await _conn.OpenAsync(cancellationToken).ConfigureAwait(false);
             await using var cmd = _conn.CreateCommand(conn, sql);