fix(sql): row-cap key-value and where-pair plans with a TOP/LIMIT N+1 dialect seam (R06:S-1)

Key-value and where-pair plans had no row limit, so a selector pointed at a history
or events table materialised every matching row on every poll. ISqlDialect gains
RowLimitPrefix/RowLimitSuffix(n) (SQL Server TOP (n), Postgres LIMIT n, Oracle FETCH
FIRST n ROWS ONLY); plans carry a RowCap (distinct keys, or 1) and ask for RowCap+1
rows; the reader also stops client-side at RowCap+1. Getting the extra row proves the
selector ambiguous: the group publishes BadConfigurationError with a rate-limited
warning. The reader reports those answered refusals so the driver counts them as
answer evidence, and any refusal-only poll now restores Healthy after a comms fault.

Refs #744
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql.Tests/PostgresDialectTests.cs

@@ -226,6 +226,15 @@ public class PostgresDialectTests
         d.ListColumnsSql.ShouldContain("\"IS_NULLABLE\"");
     }
 
+    [Fact]
+    public void RowLimit_isLimitN_inTheSuffixPosition()
+    {
+        var d = new PostgresDialect();
+        d.RowLimitPrefix(3).ShouldBe("");
+        d.RowLimitSuffix(3).ShouldBe(" LIMIT 3");
+        Should.Throw<ArgumentOutOfRangeException>(() => d.RowLimitSuffix(0));
+    }
+
     [Fact]
     public void SingleRowLimit_isLimit1_inTheSuffixPosition_withItsOwnLeadingSpace()
     {