refactor(sql): split ISqlDialect/SqlServerDialect into a .Dialect leaf (#526)

`Driver.Sql.Browser` referenced the runtime `Driver.Sql` project. The AdminUI
references that browser, so the whole SQL driver runtime — and
`ZB.MOM.WW.OtOpcUa.Core` through it — sat in the AdminUI's build/deploy graph.
This is the same layering violation #512 removed from the MQTT browser, in a
second driver, and it is why #512's expected removal of `Core.dll` from the
AdminUI's output did not happen.

MEASURED, both directions, on a clean AdminUI build:

  before: ZB.MOM.WW.OtOpcUa.Core.dll + ZB.MOM.WW.OtOpcUa.Driver.Sql.dll present
  after:  both absent

The old csproj comment's premise was sound and survives — the dialect's catalog
SQL *is* the browse engine, so it must be shared rather than duplicated. What
was wrong was the conclusion that sharing it required referencing the runtime
driver. `ISqlDialect`/`SqlServerDialect` depend on nothing in `Driver.Sql`, so
they move to a `.Dialect` leaf that both consume.

This is the `.Transport` shape, not the cheap one: `ISqlDialect` exposes
`DbProviderFactory` and `SqlServerDialect` returns `SqlClientFactory.Instance`,
so `.Contracts` (deliberately provider-free) cannot hold them. Assembly name is
`.Dialect`; the NAMESPACE stays `ZB.MOM.WW.OtOpcUa.Driver.Sql`, matching the
`Driver.Mqtt.Transport` precedent — the extraction cost zero `using` changes.

Two dependencies the cut edge surfaced as the implicit ones they were:

- The AdminUI itself read `SqlDriver.DriverTypeName` in three places — the tag
  editor map, the tag config validator, and the Sql address picker. All three
  now read `DriverTypeNames.Sql`, which is exactly what that constant resolves
  to and exactly the repoint `SqlDriverBrowser`'s own comment had deferred
  until a factory was registered against the shared constant. One exists now.
- `SqlDriverFormContractTests` asserts the AdminUI form's emitted JSON against
  the runtime factory that reads it, so it genuinely needs the runtime driver.
  `AdminUI.Tests` now references it explicitly. A test project referencing a
  runtime driver is fine — tests are not in the AdminUI's deploy graph.

New guard: `DriverBrowserLayeringTests` (Commons.Tests) scans the csproj graph
of every `*.Browser` project in the tree, transitively. It reads csproj files
rather than loaded assemblies because the cost is a build-graph cost — the
compiler emits no assembly reference for an unused `ProjectReference`, so
`MqttBrowserLayeringTests`' assembly-reference approach cannot see that case.
The two are complementary and each now points at the other.

Falsified three ways, each red then green again: the direct reference re-added
to the browser; the same reference one hop out via `.Dialect` (proving the walk
is really transitive); and both controls — browsers-discovered and
references-parsed — which exist so an empty discovery cannot pass the absence
assertion vacuously.

#526's claim that the reference "carries no comment at all" was wrong; it
carried a detailed one from the scaffold commit. Corrected on the issue and in
the design doc's project table, which had recorded the deviation as deliberate.

Claude-Session: https://claude.ai/code/session_015p7wGqy3YpZNCpDzTpGMKo

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql.Browser/SqlDriverBrowser.cs

@@ -4,6 +4,7 @@ using System.Text.Json.Serialization;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Commons.Browsing;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Driver.Sql.Contracts;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.Sql.Browser;
@@ -100,12 +101,14 @@ public sealed class SqlDriverBrowser : IDriverBrowser
 
     /// <inheritdoc />
     /// <remarks>
-    ///     Sourced from <see cref="SqlDriver.DriverTypeName"/>, the driver's interim local constant, rather
-    ///     than from <c>DriverTypeNames</c> — the shared constant set is added by the driver-factory task,
-    ///     because adding a member there reddens <c>DriverTypeNamesGuardTests</c> until a factory is
-    ///     registered against it. Repointing that one constant repoints this too.
+    ///     Sourced from the shared <see cref="DriverTypeNames"/> set, which is what the driver's own
+    ///     <c>SqlDriver.DriverTypeName</c> resolves to. This used to read that interim local constant, and
+    ///     the comment here said so; repointing it was deferred until a factory was registered against
+    ///     <see cref="DriverTypeNames.Sql"/> (else <c>DriverTypeNamesGuardTests</c> goes red). One exists
+    ///     now, and reading the shared constant is also what lets this browser stay off the runtime driver
+    ///     — <c>SqlDriver</c> is the only type it still needed from there (Gitea #526).
     /// </remarks>
-    public string DriverType => SqlDriver.DriverTypeName;
+    public string DriverType => DriverTypeNames.Sql;
 
     /// <summary>The environment variable a <c>connectionStringRef</c> resolves through.</summary>
     /// <param name="connectionStringRef">The authored reference name.</param>