feat(sql): construct Postgres and Oracle providers; MySql/Odbc stay reserved

Widens the two provider gates so an authored `{"provider":"Postgres"}` or
`{"provider":"Oracle"}` binds that provider's own dialect instead of failing
"not available in this build":

- `SqlDriverFactoryExtensions.CreateDialect` gains a Postgres and an Oracle
  arm. There is deliberately no fallback arm — a default resolving to
  SqlServerDialect would construct happily and then emit T-SQL at a Postgres
  or Oracle server. The rejection message now names the three supported and
  the two still-reserved providers.
- `SqlDriverBrowser.DefaultDialectSelector` widens identically, so a provider
  the runtime constructs is also browsable; MySql/Odbc keep resolving to null
  and the caller keeps reporting them as unavailable.

Tests: the existing rejected-provider controls flip from Postgres to MySql
(factory) and Odbc (browser) so the reserved half stays falsifiable, and the
new legs assert the bound dialect TYPE rather than mere construction —
"no throw" alone would pass against a SqlServer fallback.

Doc-comment sweep (contract addition, one line each): the "v1 constructs
SqlServer only" / "reserved for P2" claims in SqlProvider, SqlDriverConfigDto,
ISqlDialect.Provider and SqlServerDialect are now false and were corrected in
the same change.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql.Contracts/SqlDriverConfigDto.cs

@@ -16,7 +16,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Sql.Contracts;
 /// </summary>
 public sealed class SqlDriverConfigDto
 {
-    /// <summary>Which ADO.NET provider/dialect backs this instance. Defaults to <see cref="SqlProvider.SqlServer"/> — the only provider v1 constructs.</summary>
+    /// <summary>Which ADO.NET provider/dialect backs this instance. Defaults to <see cref="SqlProvider.SqlServer"/>; <see cref="SqlProvider.Postgres"/> and <see cref="SqlProvider.Oracle"/> are also constructed.</summary>
     public SqlProvider Provider { get; init; } = SqlProvider.SqlServer;
 
     /// <summary>