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/QuestDbConnection.cs

@@ -1,4 +1,6 @@
 using System.Net.Sockets;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
 using Npgsql;
 using NpgsqlTypes;
 
@@ -12,8 +14,15 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.QuestDb;
 ///     failures with <see cref="IsTransient"/> / <see cref="IsAlreadyExists"/>. Every QuestDB server error carries
 ///     SQLSTATE <c>00000</c>, so classification is by message text, never by SQLSTATE.</para>
 /// </summary>
-internal sealed class QuestDbConnection : IAsyncDisposable
+internal sealed class QuestDbConnection : IAsyncDisposable, IDisposable
 {
+    /// <summary>
+    ///     Npgsql pool cap applied when the connection string does not set <c>Maximum Pool Size</c> itself. Npgsql's own
+    ///     default (100) exceeds QuestDB's default PG-wire connection limit (64), and the server's default read
+    ///     concurrency alone can reach 64; an explicit value in the connection string is always kept.
+    /// </summary>
+    internal const int DefaultMaxPoolSize = 24;
+
     private static readonly long MinSafeTicks = 10;                                   // DateTime.MinValue itself binds as -infinity
     private static readonly long MaxSafeTicks = DateTime.MaxValue.Ticks - DateTime.MaxValue.Ticks % 10; // MaxValue itself binds as +infinity
 
@@ -21,14 +30,40 @@ internal sealed class QuestDbConnection : IAsyncDisposable
 
     /// <summary>Creates the connection helper; options must already be valid.</summary>
     /// <param name="options">Validated options.</param>
-    public QuestDbConnection(QuestDbHistorianOptions options)
+    /// <param name="log">Optional logger; the effective pool size is logged once at Information.</param>
+    public QuestDbConnection(QuestDbHistorianOptions options, ILogger? log = null)
     {
         ArgumentNullException.ThrowIfNull(options);
         if (!QuestDbHistorianOptions.IsValidPrefix(options.TablePrefix))
             throw new ArgumentException("Invalid table prefix.", nameof(options));
         TablePrefix = options.TablePrefix;
         CommandTimeoutSeconds = Math.Max(1, (int)Math.Ceiling(options.CommandTimeout.TotalSeconds));
-        _dataSource = new NpgsqlDataSourceBuilder(options.ConnectionString).Build();
+        var csb = new NpgsqlConnectionStringBuilder(options.ConnectionString);
+        var explicitPool = HasExplicitMaxPoolSize(options.ConnectionString);
+        if (!explicitPool) csb.MaxPoolSize = DefaultMaxPoolSize;
+        EffectiveMaxPoolSize = csb.MaxPoolSize;
+        (log ?? NullLogger.Instance).LogInformation(
+            "QuestDB historian connection pool: Maximum Pool Size = {MaxPoolSize} ({Source}).",
+            EffectiveMaxPoolSize, explicitPool ? "from the connection string" : "default cap");
+        _dataSource = new NpgsqlDataSourceBuilder(csb.ConnectionString).Build();
+    }
+
+    /// <summary>The Npgsql <c>Maximum Pool Size</c> in effect (the connection string's own value, else <see cref="DefaultMaxPoolSize"/>).</summary>
+    internal int EffectiveMaxPoolSize { get; }
+
+    // Npgsql accepts "Maximum Pool Size" and "MaxPoolSize" (case-insensitive); a generic parse keeps the caller's own
+    // keywords so "was it set" is answered by the string itself, not by the builder's default.
+    private static bool HasExplicitMaxPoolSize(string connectionString)
+    {
+        var generic = new System.Data.Common.DbConnectionStringBuilder { ConnectionString = connectionString };
+        foreach (string key in generic.Keys)
+        {
+            var k = key.Replace(" ", "", StringComparison.Ordinal);
+            if (string.Equals(k, "MaxPoolSize", StringComparison.OrdinalIgnoreCase)
+                || string.Equals(k, "MaximumPoolSize", StringComparison.OrdinalIgnoreCase))
+                return true;
+        }
+        return false;
     }
 
     /// <summary>The validated table prefix.</summary>
@@ -70,6 +105,9 @@ internal sealed class QuestDbConnection : IAsyncDisposable
     /// <inheritdoc/>
     public ValueTask DisposeAsync() => _dataSource.DisposeAsync();
 
+    /// <inheritdoc/>
+    public void Dispose() => _dataSource.Dispose();
+
     // ---- timestamps (R6) -------------------------------------------------------------------------------------------
 
     /// <summary>