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>

src/Strata.SqlTools.Markdown/SqlServer/QueryBreakdownGenerator.cs

@@ -201,7 +201,7 @@ public class QueryBreakdownGenerator
             return text;
         }
 
-        return text.Substring(0, maxLength) + "...";
+        return string.Concat(text.AsSpan(0, maxLength), "...");
     }
 }