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/Server/ZB.MOM.WW.OtOpcUa.Host/Program.cs

@@ -235,15 +235,19 @@ if (hasDriver)
     // Backend selection: resolve the provider once (unknown name => OptionsValidationException naming the
     // allowed values) and build every historian seam through it.
     var historianProvider = HistorianBackendRegistry.Resolve(serverHistorianOptions, builder.Configuration);
-    builder.Services.AddSingleton<IHistorianBackendProvider>(historianProvider);
+    // Registered through a factory (not as an instance) so the container owns it and disposes it at shutdown
+    // (the QuestDb provider's shared Npgsql pool); every seam below resolves the provider from the container
+    // rather than capturing the local, so whichever seam builds the backend's shared state also makes the
+    // container track the provider for disposal.
+    builder.Services.AddSingleton<IHistorianBackendProvider>(_ => historianProvider);
     // HistoryUpdate is gated like HistoryRead: None unconditionally, the real holder only when enabled.
     builder.Services.AddSingleton(HistorianUpdaterHolder.None);
     if (serverHistorianOptions.Enabled)
-        builder.Services.AddSingleton(sp => new HistorianUpdaterHolder(historianProvider.CreateUpdater(sp)));
+        builder.Services.AddSingleton(sp => new HistorianUpdaterHolder(sp.GetRequiredService<IHistorianBackendProvider>().CreateUpdater(sp)));
 
     builder.Services.AddAlarmHistorian(
         builder.Configuration,
-        (_, sp) => historianProvider.CreateAlarmWriter(sp));
+        (_, sp) => sp.GetRequiredService<IHistorianBackendProvider>().CreateAlarmWriter(sp));
 
     // Node-local LocalDb: caches the deployed-configuration artifact so this node can boot from
     // its last-known-good config when central SQL is unreachable, and optionally replicates that
@@ -269,7 +273,7 @@ if (hasDriver)
     // node manager's HistoryRead overrides block-bridge to. Runtime owns the gating.
     builder.Services.AddServerHistorian(
         builder.Configuration,
-        (_, sp) => historianProvider.CreateDataSource(sp));
+        (_, sp) => sp.GetRequiredService<IHistorianBackendProvider>().CreateDataSource(sp));
 
     // Config-gated historian tag provisioning. When the ServerHistorian section is enabled this registers the
     // selected backend's provisioner (GatewayTagProvisioner -> the gateway's EnsureTags, or the SqlServer Tag-row
@@ -280,7 +284,7 @@ if (hasDriver)
     // the SAME ServerHistorian:Enabled flag as the read path — both use the one resolved backend.
     builder.Services.AddHistorianProvisioning(
         builder.Configuration,
-        (_, sp) => historianProvider.CreateProvisioning(sp));
+        (_, sp) => sp.GetRequiredService<IHistorianBackendProvider>().CreateProvisioning(sp));
 
     // Continuous historization of driver (non-Galaxy) tag values. Gated on ContinuousHistorization:Enabled
     // AND ServerHistorian:Enabled: the recorder drains driver-tag live values through the selected backend's
@@ -319,7 +323,7 @@ if (hasDriver)
         // The backend's live-value writer. On Gateway it opens its OWN gRPC channel to the same gateway (a second
         // channel to a co-located sidecar is cheap — the gateway pools the historian sessions server-side); on
         // SqlServer it shares the provider's connection helper, schema bootstrapper and tag catalog.
-        builder.Services.AddSingleton<IHistorianValueWriter>(sp => historianProvider.CreateValueWriter(sp));
+        builder.Services.AddSingleton<IHistorianValueWriter>(sp => sp.GetRequiredService<IHistorianBackendProvider>().CreateValueWriter(sp));
     }
 
     // Bind every cross-platform driver factory before AddAkka resolves IDriverFactory — replaces