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.Snowflake/Breakdowns/QueryBreakdown.cs

@@ -141,7 +141,7 @@ public class QueryBreakdown : SqlServerQueryBreakdown
 
         if (parameterName.StartsWith('@'))
         {
-            return ":" + parameterName.Substring(1);
+            return string.Concat(":", parameterName.AsSpan(1));
         }
 
         // Add : prefix
@@ -159,7 +159,7 @@ public class QueryBreakdown : SqlServerQueryBreakdown
             if (paramName.StartsWith(':'))
             {
                 // Add @param version
-                var atParam = "@" + paramName.Substring(1);
+                var atParam = string.Concat("@", paramName.AsSpan(1));
                 if (!Parameters.ContainsKey(atParam))
                 {
                     Parameters[atParam] = Parameters[paramName];
@@ -168,7 +168,7 @@ public class QueryBreakdown : SqlServerQueryBreakdown
             else if (paramName.StartsWith('@'))
             {
                 // Add :param version
-                var colonParam = ":" + paramName.Substring(1);
+                var colonParam = string.Concat(":", paramName.AsSpan(1));
                 if (!Parameters.ContainsKey(colonParam))
                 {
                     Parameters[colonParam] = Parameters[paramName];
@@ -539,7 +539,7 @@ public class QueryBreakdown : SqlServerQueryBreakdown
 
                 if (i > 0)
                 {
-                    sb.Append(",");
+                    sb.Append(',');
                     sb.AppendLine();
                 }