feat(historian): Part 11 modified-value history on SqlServer + QuestDB (#668)

Every HistoryUpdate a SQL backend applies now leaves a modification trail
(prior value, principal, Part 11 update type, modification time), and
HistoryReadRaw with IsReadModified=true serves it as HistoryModifiedData.

- Core: HistoryUpdateContext threaded into all three IHistorianDataUpdater
  methods; IHistorianDataSource.ReadModifiedAsync (default NotSupported =>
  BadHistoryOperationUnsupported on Gateway/Null); HistoryModified* contracts.
- SqlServer: schema v2 (002_sample_modified.sql, RequiredVersion=2, docs copy);
  trail written by OUTPUT ... INTO on the same MERGE/DELETE statement, so a
  failed update leaves no audit row; retention purges SampleModified per tag on
  the source-time cutoff; ReadModifiedAsync keyed on (SourceTimeUtc, ModifiedId).
- QuestDB: append-only {prefix}sample_modified (TTL like samples), trail row
  written BEFORE the change (orphan-on-crash, never an untracked change);
  existence reads now carry the prior value; ReadModifiedAsync.
- Node manager: modified reads dispatch + page via the #669 continuation store
  (HistoryContinuationState gains HistoryCursorKind + LastModifiedId), gated by
  the existing HistoryRead decision; session principal / key id passed to the
  updater. IsDeleteModified stays unsupported.
- Client.CLI: historyread --modified.
- Tests: node-manager dispatch/paging/cursor binding/principal threading,
  over-the-wire HistoryModifiedData, shared ModifiedValueConformance on both
  backends, SqlServer atomicity (forced trail failure => no change) + v1->v2
  upgrade + retention trail purge.
- Docs: Historian.md (Modified-value history section, schema v2 upgrade note),
  security.md, Client.CLI.md, CLAUDE.md.

src/Client/ZB.MOM.WW.OtOpcUa.Client.Shared/Adapters/DefaultSessionAdapter.cs

@@ -206,6 +206,74 @@ internal sealed class DefaultSessionAdapter : ISessionAdapter
         return allValues;
     }
 
+    /// <inheritdoc />
+    public async Task<IReadOnlyList<Models.HistoryModifiedEntry>> HistoryReadModifiedAsync(
+        NodeId nodeId, DateTime startTime, DateTime endTime, int maxValues, CancellationToken ct)
+    {
+        var details = new ReadRawModifiedDetails
+        {
+            StartTime = startTime,
+            EndTime = endTime,
+            NumValuesPerNode = (uint)maxValues,
+            IsReadModified = true,
+            ReturnBounds = false
+        };
+
+        var nodesToRead = new HistoryReadValueIdCollection
+        {
+            new HistoryReadValueId { NodeId = nodeId }
+        };
+
+        var all = new List<Models.HistoryModifiedEntry>();
+        byte[]? continuationPoint = null;
+
+        do
+        {
+            if (continuationPoint != null)
+                nodesToRead[0].ContinuationPoint = continuationPoint;
+
+            var response = await _session.HistoryReadAsync(
+                null,
+                new ExtensionObject(details),
+                TimestampsToReturn.Both,
+                false,
+                nodesToRead,
+                ct).ConfigureAwait(false);
+
+            var results = response.Results;
+            if (results == null || results.Count == 0)
+                break;
+
+            var result = results[0];
+            HistoryReadStatus.ThrowIfRefused(result.StatusCode, nodeId);
+
+            if (result.HistoryData is ExtensionObject ext && ext.Body is HistoryModifiedData modified)
+            {
+                for (var i = 0; i < modified.DataValues.Count; i++)
+                {
+                    var info = i < modified.ModificationInfos.Count ? modified.ModificationInfos[i] : null;
+                    all.Add(new Models.HistoryModifiedEntry(
+                        modified.DataValues[i],
+                        info?.ModificationTime ?? DateTime.MinValue,
+                        info?.UpdateType ?? default,
+                        info?.UserName));
+                }
+            }
+
+            continuationPoint = result.ContinuationPoint;
+        } while (continuationPoint != null && continuationPoint.Length > 0 && all.Count < maxValues);
+
+        // A read stopped by the client's own cap leaves a server cursor behind; release it.
+        if (continuationPoint is { Length: > 0 })
+        {
+            nodesToRead[0].ContinuationPoint = continuationPoint;
+            await _session.HistoryReadAsync(null, new ExtensionObject(details), TimestampsToReturn.Both, true,
+                nodesToRead, ct).ConfigureAwait(false);
+        }
+
+        return all;
+    }
+
     /// <inheritdoc />
     public async Task<IReadOnlyList<DataValue>> HistoryReadAggregateAsync(
         NodeId nodeId, DateTime startTime, DateTime endTime, NodeId aggregateId, double intervalMs,