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/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.SqlServer/SqlServerSchemaBootstrapper.cs

@@ -14,12 +14,16 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.SqlServer;
 ///     <see cref="BootstrapFailureCache.DefaultDuration"/> retries (<see cref="BootstrapFailureCache"/>). Within that window the last failure is re-thrown without touching
 ///     SQL, so a missing schema (or a SQL outage) does not serialise every write, read and alarm event behind one
 ///     semaphore and one round-trip each.
-///     With <c>AutoCreateSchema=false</c> it only verifies <c>MAX(Version) &gt;= 1</c>.
+///     With <c>AutoCreateSchema=false</c> it only verifies <c>MAX(Version) &gt;= </c><see cref="RequiredVersion"/>.
 /// </summary>
 internal sealed partial class SqlServerSchemaBootstrapper
 {
-    /// <summary>The schema version this build requires.</summary>
-    public const int RequiredVersion = 1;
+    /// <summary>
+    ///     The schema version this build requires: 2 = <c>002_sample_modified.sql</c> (Part 11 modified-value
+    ///     history, Gitea #668). An existing v1 schema is upgraded in place on the next bootstrap when
+    ///     <c>AutoCreateSchema</c> is on; otherwise the script must be applied by hand.
+    /// </summary>
+    public const int RequiredVersion = 2;
 
     private const string LockResource = "OtOpcUaHistorianSchema";
     private const int LockTimeoutMs = 30_000;
@@ -48,7 +52,7 @@ internal sealed partial class SqlServerSchemaBootstrapper
     /// <summary>Ensures the schema is ready; no-op after the first success.</summary>
     /// <param name="ct">Cancellation.</param>
     /// <returns>A task completing when the schema is usable.</returns>
-    /// <exception cref="HistorianSchemaMissingException">AutoCreateSchema is false and version 1 is absent.</exception>
+    /// <exception cref="HistorianSchemaMissingException">AutoCreateSchema is false and <see cref="RequiredVersion"/> is absent.</exception>
     public async Task EnsureAsync(CancellationToken ct)
     {
         if (_ready) return;
@@ -94,7 +98,7 @@ internal sealed partial class SqlServerSchemaBootstrapper
         if (v < RequiredVersion)
             throw new HistorianSchemaMissingException(
                 $"Historian schema [{_conn.Schema}] is missing version {RequiredVersion} (found {v}) and AutoCreateSchema is false. " +
-                "Apply docs/historian/sqlserver/001_initial.sql or enable AutoCreateSchema.");
+                "Apply the docs/historian/sqlserver/NNN_*.sql scripts above version " + v + " in order, or enable AutoCreateSchema.");
     }
 
     private async Task ApplyAsync(SqlConnection conn, CancellationToken ct)