chore(sonar): bulk-fix mechanical CA/IDE analyzer warnings

Applied via `dotnet format analyzers --diagnostics IDE0028 CA1825 CA1834
CA1845 CA1847 CA1860 CA1866 CA1853 CA1830 CA1846 CA1806 CA1869 CA2249
--severity info`. 19 files touched, all mechanical syntactic rewrites:

- CA1847: string.Contains("x") -> string.Contains('x')
- CA2249: s.IndexOf(c) == -1 -> !s.Contains(c)
- CA1830: sb.Append(sb.ToString()) -> sb.Append(sb)
- CA1834: StringBuilder.Append("x") -> Append('x')
- CA1825, CA1860, CA1866, CA1853, IDE0028, CA1845: corresponding fixers

Three rules in the batch had no batch fixer available (CA1846 ×4,
CA1806 ×1, CA1869 ×1) and stay open for separate manual handling.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Strata.SqlTools.SqlServer.Tests/SqlServer/RecursiveCTETests.cs

@@ -174,7 +174,7 @@ public class RecursiveCTETests
         var merged = mainQuery.GetMergedParameters();
 
         // Assert
-        var statusKey = merged.Keys.FirstOrDefault(k => k.Contains("Status") && !k.Contains("@") && !k.Contains("$"));
+        var statusKey = merged.Keys.FirstOrDefault(k => k.Contains("Status") && !k.Contains('@') && !k.Contains('$'));
         Assert.That(statusKey, Is.Not.Null);
         Assert.That(merged[statusKey], Is.EqualTo("active"), "Main query parameter should take precedence");
     }