fix(historian): #668 review follow-ups (explicit modified source time, paging tests, ACL test, QuestDB orphan warning, docs)

- HistoryModifiedValue gains explicit SourceTimeUtc (SqlServer + QuestDB populate it); the node manager's resume cursor uses it instead of the prior value's nullable source timestamp (MinValue for inserts).
- ACL test now uses a trail-returning data source and asserts Good + data on the allow leg.
- Node-manager tests: end-only backward open-ended paging, reverse resume cursor, null-prior cursor.
- QuestDB updater logs a Warning (tag + time range) when a sample write fails after its trail rows landed.
- docs/Historian.md: rolling-upgrade window, IDENTITY-vs-commit ordering, QuestDB cross-node ModifiedId clock ordering.

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

@@ -212,7 +212,7 @@ public sealed class SqlServerHistorianDataSource : IHistorianDataSource
                     }
 
                     values.Add(new HistoryModifiedValue(
-                        prior, modifiedAt, (HistoryModificationType)reader.GetByte(9), reader.GetString(10), reader.GetInt64(7)));
+                        prior, modifiedAt, (HistoryModificationType)reader.GetByte(9), reader.GetString(10), reader.GetInt64(7), sourceTime));
                 }
             }