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/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/HistoryPaging.cs

@@ -46,6 +46,11 @@ namespace ZB.MOM.WW.OtOpcUa.OpcUaServer;
 ///     <see cref="HistoryCursorKind.Modified"/> only: the normalised window start, so a resumed page keeps the original
 ///     window and direction (the modified read resumes by key, not by moving the window start).
 /// </param>
+/// <param name="Reverse">
+///     <see cref="HistoryCursorKind.Events"/> only (Gitea #675): the read is newest-first over
+///     <c>(EndUtc, NextStartUtc]</c>. A resumed events read takes its direction from here, never from the resume
+///     request's details. Raw keeps deriving it from the window (<c>NextStartUtc &gt; EndUtc</c>).
+/// </param>
 internal sealed record HistoryContinuationState(
     string Tagname,
     DateTime NextStartUtc,
@@ -54,7 +59,8 @@ internal sealed record HistoryContinuationState(
     uint NumValuesPerNode,
     HistoryCursorKind Kind = HistoryCursorKind.Raw,
     long LastModifiedId = 0,
-    DateTime WindowStartUtc = default);
+    DateTime WindowStartUtc = default,
+    bool Reverse = false);
 
 /// <summary>The HistoryRead kind that issued a <see cref="HistoryContinuationState"/>.</summary>
 internal enum HistoryCursorKind