chore(sonar)!: mark instance-data-free members static (CA1822)

Applied via `dotnet format analyzers --diagnostics CA1822 --severity info`.
12 files touched. The fixer also updated internal callers in tests to use
the type-name form (e.g. `gen.Method(x)` -> `Generator.Method(x)`); build
and full test suite remain green.

BREAKING CHANGE: two public methods become static and therefore can no
longer be invoked through an instance reference by external consumers:
- Strata.SqlTools.Markdown.LinqToSql.QueryBreakdownGenerator.GenerateMethodChainDiagram
- Strata.SqlTools.Markdown.LinqToSql.SqlStatementGenerator.GenerateLinqPipelineDiagram

Both are stateless utility methods on Generator classes — the static form
is the correct shape; the only callers in this repo already used the
type-name form. External code should change `gen.GenerateMethodChainDiagram(...)`
to `QueryBreakdownGenerator.GenerateMethodChainDiagram(...)`.

All other CA1822 hits in this commit are on private/protected members
(no public-surface impact).

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

src/Strata.SqlTools.Markdown/Expressions/ExpressionGenerator.cs

@@ -260,7 +260,7 @@ public class ExpressionGenerator : IVisitor<string>
         return sb.ToString();
     }
 
-    private int GenerateMermaidNodes(Expression expression, StringBuilder sb, Dictionary<object, int> nodeMap, ref int nodeCounter)
+    private static int GenerateMermaidNodes(Expression expression, StringBuilder sb, Dictionary<object, int> nodeMap, ref int nodeCounter)
     {
         var currentNode = nodeCounter++;
         nodeMap[expression] = currentNode;