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.QuestDb/QuestDbHistorianDataSource.cs

@@ -361,8 +361,18 @@ public sealed class QuestDbHistorianDataSource : IHistorianDataSource
     ///     <c>maxEvents + 1</c> rows are fetched; when the extra row arrives it is dropped and the continuation point is
     ///     the UTF-8 of <see cref="EventContinuation.Encode"/> for that first not-returned event.
     /// </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 the (rounded) <c>(lo, hi]</c> ordered by
+    ///     <c>(ts, event_id)</c> DESCENDING, so <c>LIMIT</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 limit, so an over-long filter matches nothing.
         if (sourceName is not null && sourceName.Length > HistorianTagNames.MaxLength)
@@ -376,9 +386,9 @@ public sealed class QuestDbHistorianDataSource : IHistorianDataSource
             var bounded = maxEvents > 0 && maxEvents < int.MaxValue;
             var sql =
                 $"SELECT event_id, source, ts, received_utc, message, severity FROM {_conn.EventTable} " +
-                "WHERE ts >= $1 AND ts < $2" +
+                (reverse ? "WHERE ts > $1 AND ts <= $2" : "WHERE ts >= $1 AND ts < $2") +
                 (sourceName is null ? "" : " AND source = $3") +
-                " ORDER BY ts ASC, event_id ASC" +
+                (reverse ? " ORDER BY ts DESC, event_id DESC" : " ORDER BY ts ASC, event_id ASC") +
                 (bounded ? (sourceName is null ? " LIMIT $3" : " LIMIT $4") : "");
 
             await using var conn = await _conn.OpenAsync(cancellationToken).ConfigureAwait(false);