fix(historian): QuestDB final-review fix wave (I-1, M-1, M-3, M-5, M-8, M-9)

- I-1: QuestDbConnection caps Npgsql Maximum Pool Size at 24 (DefaultMaxPoolSize)
  when the connection string does not set it; an explicit value is kept. The
  effective value is logged once at Information.
- M-1: QuestDbTagCatalog.EnsureAsync waits for the tag table's sequenced commits
  and re-checks before inserting, so it no longer overwrites a provisioner row
  (unit/description) that is committed but not yet applied. Integration test
  reproduces the clobber against real QuestDB (falsified).
- M-3: the pre-1970 drop Warning is rate-limited per tag (once per 10 min);
  DroppedPre1970 still counts every sample.
- M-5: QuestDbHistorianProvider is IAsyncDisposable/IDisposable and disposes the
  shared Npgsql pool; Program.cs registers the provider through a factory and
  every seam resolves it from the container, so DI disposes it at shutdown.
- M-8, M-9: docs fixes (HistoryUpdate transaction wording; folded duplicate
  HistoryUpdate paragraph). Pool-size docs updated for the new default cap.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.QuestDb/QuestDbHistorianProvider.cs

@@ -18,8 +18,10 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.QuestDb;
 ///     validation and no I/O, so resolving the provider for a backend nobody consumes never fails on its options
 ///     (they are validated, consumer-gated, by the host's <c>ServerHistorianOptionsValidator</c>). The first
 ///     <c>Create*</c> call's service provider supplies the logger factory the shared pieces log through.
+///     <para>The provider owns the shared connection pool and disposes it (IAsyncDisposable/IDisposable); the host
+///     registers the provider through a DI factory so the container disposes it at shutdown.</para>
 /// </remarks>
-public sealed class QuestDbHistorianProvider : IHistorianBackendProvider
+public sealed class QuestDbHistorianProvider : IHistorianBackendProvider, IAsyncDisposable, IDisposable
 {
     private static readonly FrozenSet<HistorianValueKind> Kinds =
         Enum.GetValues<HistorianValueKind>().ToFrozenSet();
@@ -27,6 +29,7 @@ public sealed class QuestDbHistorianProvider : IHistorianBackendProvider
     private readonly QuestDbHistorianOptions _options;
     private readonly object _initLock = new();
     private Shared? _shared;
+    private bool _disposed;
 
     /// <summary>Creates the provider over the <c>ServerHistorian:QuestDb</c> options (validated elsewhere).</summary>
     /// <param name="options">The <c>ServerHistorian:QuestDb</c> options.</param>
@@ -51,7 +54,8 @@ public sealed class QuestDbHistorianProvider : IHistorianBackendProvider
         {
             if (_shared is { } raced) return raced;
             var loggers = Loggers(sp);
-            var conn = new QuestDbConnection(_options);
+            ObjectDisposedException.ThrowIf(_disposed, this);
+            var conn = new QuestDbConnection(_options, loggers.CreateLogger<QuestDbConnection>());
             var bootstrap = new QuestDbSchemaBootstrapper(conn, _options, loggers.CreateLogger<QuestDbSchemaBootstrapper>());
             var wal = new QuestDbWalVisibility(conn, _options.VisibilityTimeout, loggers.CreateLogger<QuestDbWalVisibility>());
             var shared = new Shared(conn, bootstrap, new QuestDbTagCatalog(conn, bootstrap, wal), wal);
@@ -101,6 +105,28 @@ public sealed class QuestDbHistorianProvider : IHistorianBackendProvider
             Loggers(sp).CreateLogger<QuestDbHistorianDataUpdater>());
     }
 
+    /// <summary>Disposes the shared connection pool, when one was built. Idempotent.</summary>
+    /// <returns>A task completing when the pool is disposed.</returns>
+    public async ValueTask DisposeAsync()
+    {
+        if (TakeForDispose() is { } conn) await conn.DisposeAsync().ConfigureAwait(false);
+    }
+
+    /// <summary>Disposes the shared connection pool, when one was built. Idempotent.</summary>
+    public void Dispose() => TakeForDispose()?.Dispose();
+
+    private QuestDbConnection? TakeForDispose()
+    {
+        lock (_initLock)
+        {
+            if (_disposed) return null;
+            _disposed = true;
+            var conn = _shared?.Conn;
+            _shared = null;
+            return conn;
+        }
+    }
+
     private sealed record Shared(
         QuestDbConnection Conn, QuestDbSchemaBootstrapper Bootstrap, QuestDbTagCatalog Catalog, QuestDbWalVisibility Wal);
 }