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

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql.Dialect/OracleDialect.cs

@@ -124,6 +124,21 @@ public sealed class OracleDialect : ISqlDialect
     // statement shape, which this seam deliberately leaves with the planner.
     public string SingleRowLimitSuffix => " FETCH FIRST 1 ROWS ONLY";
 
+    /// <inheritdoc />
+    public string RowLimitPrefix(int rows)
+    {
+        ArgumentOutOfRangeException.ThrowIfLessThan(rows, 1);
+        return string.Empty;
+    }
+
+    /// <inheritdoc />
+    // The same 12c+ row-limiting clause as SingleRowLimitSuffix; valid after a WHERE with no ORDER BY.
+    public string RowLimitSuffix(int rows)
+    {
+        ArgumentOutOfRangeException.ThrowIfLessThan(rows, 1);
+        return " FETCH FIRST " + rows.ToString(System.Globalization.CultureInfo.InvariantCulture) + " ROWS ONLY";
+    }
+
     /// <inheritdoc />
     // Schemas visible to the connecting principal, from ALL_USERS (Oracle equates a schema with a
     // user), aliased to the TABLE_SCHEMA column name the catalog readers project by.