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.Browser/SqlDriverBrowser.cs

@@ -80,8 +80,8 @@ public sealed class SqlDriverBrowser : IDriverBrowser
     /// <param name="dialectSelector">
     ///     Maps an authored <see cref="SqlProvider"/> onto the dialect that browses it, or <see langword="null"/>
     ///     for a provider this build does not carry. Defaults to <see cref="DefaultDialectSelector"/>
-    ///     (SqlServer only, in v1). A constructor parameter rather than a test hatch: it is also how a P2
-    ///     provider gets added without touching this class.
+    ///     (SqlServer, Postgres and Oracle). A constructor parameter rather than a test hatch: it is also how
+    ///     a further provider gets added without touching this class.
     /// </param>
     /// <param name="environmentReader">
     ///     Reads one environment variable. Defaults to <see cref="Environment.GetEnvironmentVariable(string)"/>.
@@ -117,14 +117,23 @@ public sealed class SqlDriverBrowser : IDriverBrowser
         ConnectionStringEnvironmentPrefix + connectionStringRef;
 
     /// <summary>
-    ///     The providers this build can browse. v1 constructs SQL Server only; every other
-    ///     <see cref="SqlProvider"/> member is a reserved name, so it resolves to <see langword="null"/> and
-    ///     the caller reports it as unavailable rather than crashing on a null dialect.
+    ///     The providers this build can browse — SQL Server, PostgreSQL and Oracle. The remaining
+    ///     <see cref="SqlProvider"/> members (<see cref="SqlProvider.MySql"/>, <see cref="SqlProvider.Odbc"/>)
+    ///     are reserved names, so they resolve to <see langword="null"/> and the caller reports them as
+    ///     unavailable rather than crashing on a null dialect.
+    ///     <para>Kept in step with <c>SqlDriverFactoryExtensions.CreateDialect</c>: a provider the runtime
+    ///     driver constructs but the browser cannot select would leave the operator authoring tags by hand
+    ///     against a database the AdminUI refuses to show them.</para>
     /// </summary>
     /// <param name="provider">The authored provider.</param>
     /// <returns>The dialect, or <see langword="null"/> when this build does not carry the provider.</returns>
-    public static ISqlDialect? DefaultDialectSelector(SqlProvider provider) =>
-        provider == SqlProvider.SqlServer ? new SqlServerDialect() : null;
+    public static ISqlDialect? DefaultDialectSelector(SqlProvider provider) => provider switch
+    {
+        SqlProvider.SqlServer => new SqlServerDialect(),
+        SqlProvider.Postgres => new PostgresDialect(),
+        SqlProvider.Oracle => new OracleDialect(),
+        _ => null,
+    };
 
     /// <inheritdoc />
     /// <exception cref="InvalidOperationException">
@@ -143,12 +152,13 @@ public sealed class SqlDriverBrowser : IDriverBrowser
         var literal = ReadPastedConnectionString(configJson);
         var config = Deserialize(configJson, literal);
 
-        // Provider first: "this build cannot browse Postgres" is true regardless of how the database is
+        // Provider first: "this build cannot browse MySql" is true regardless of how the database is
         // named, and answering it before touching the environment keeps the two failures from masking.
         var dialect = _dialectSelector(config.Provider)
             ?? throw new InvalidOperationException(
-                $"Sql provider '{config.Provider}' is not available in this build; v1 browses "
-                + $"'{SqlProvider.SqlServer}' only.");
+                $"Sql provider '{config.Provider}' is not available in this build; browsing supports "
+                + $"'{SqlProvider.SqlServer}', '{SqlProvider.Postgres}' and '{SqlProvider.Oracle}' "
+                + $"('{SqlProvider.MySql}' and '{SqlProvider.Odbc}' are reserved names).");
 
         var reference = config.ConnectionStringRef;
         var connectionString = ResolveConnectionString(literal, reference);