chore(sonar)!: mark public Markdown generator methods static (CA1822)

Three public methods on the SqlServer-namespaced Markdown generators no
longer touch instance state and now carry the `static` keyword:

- `Markdown.SqlServer.QueryBreakdownGenerator.GenerateMermaidDiagram(QueryBreakdown, string?)`
- `Markdown.SqlServer.SqlStatementGenerator.GenerateSequenceDiagram(ISqlBreakdown, string?)`
- `Markdown.SqlServer.SqlStatementGenerator.GenerateEntityRelationshipDiagram(IEnumerable<string>, string?)`

Plus one private bonus the analyzer caught on the same pass:
- `LinqExpressionVisitor.ExtractSelectExpression` → static (non-breaking).

Internal callers in the Snowflake/LinqToSql/PostgreSql wrapper classes
and in the test fixtures are updated to the type-name form
(`SqlServer.SqlStatementGenerator.GenerateSequenceDiagram(...)`).
The wrappers retain their `_baseGenerator` field for now even though it
is no longer used — that S4487 / unused-field cleanup is its own commit.

BREAKING CHANGE: External NuGet consumers calling
`generatorInstance.GenerateMermaidDiagram(...)`,
`generatorInstance.GenerateSequenceDiagram(...)`, or
`generatorInstance.GenerateEntityRelationshipDiagram(...)` on the
SqlServer-namespaced generators must switch to type-name form, e.g.
`Markdown.SqlServer.SqlStatementGenerator.GenerateSequenceDiagram(...)`.
Calls through the Snowflake / LinqToSql / PostgreSql wrapper classes are
unaffected at the call site.

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

src/Strata.SqlTools.LinqToSql/Visitors/LinqExpressionVisitor.cs

@@ -277,7 +277,7 @@ public class LinqExpressionVisitor : ExpressionVisitor
         return base.VisitMember(node);
     }
 
-    private string ExtractSelectExpression(Expression expression)
+    private static string ExtractSelectExpression(Expression expression)
     {
         if (expression is NewExpression newExpr)
         {

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

@@ -28,7 +28,7 @@ public class QueryBreakdownGenerator
     {
         // Since LinqQueryBreakdown inherits from SqlServer.QueryBreakdown,
         // we can use the base generator which works with the shared properties
-        return _baseGenerator.GenerateMermaidDiagram(queryBreakdown, title);
+        return SqlServer.QueryBreakdownGenerator.GenerateMermaidDiagram(queryBreakdown, title);
     }
 
     /// <summary>

src/Strata.SqlTools.Markdown/LinqToSql/SqlStatementGenerator.cs

@@ -28,7 +28,7 @@ public class SqlStatementGenerator
     /// <returns>A string containing the Mermaid sequence diagram markdown.</returns>
     public string GenerateSequenceDiagram(ISqlBreakdown sqlBreakdown, string? title = null)
     {
-        return _baseGenerator.GenerateSequenceDiagram(sqlBreakdown, title);
+        return SqlServer.SqlStatementGenerator.GenerateSequenceDiagram(sqlBreakdown, title);
     }
 
     /// <summary>
@@ -49,7 +49,7 @@ public class SqlStatementGenerator
             tableNames.Add(fromClauseText);
         }
 
-        return _baseGenerator.GenerateEntityRelationshipDiagram(tableNames, title);
+        return SqlServer.SqlStatementGenerator.GenerateEntityRelationshipDiagram(tableNames, title);
     }
 
     /// <summary>

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

@@ -28,6 +28,6 @@ public class QueryBreakdownGenerator
     {
         // Since PostgreSql.QueryBreakdown inherits from SqlServer.QueryBreakdown,
         // we can use the base generator which works with the shared properties
-        return _baseGenerator.GenerateMermaidDiagram(queryBreakdown, title);
+        return SqlServer.QueryBreakdownGenerator.GenerateMermaidDiagram(queryBreakdown, title);
     }
 }

src/Strata.SqlTools.Markdown/PostgreSql/SqlStatementGenerator.cs

@@ -26,7 +26,7 @@ public class SqlStatementGenerator
     /// <returns>A string containing the Mermaid sequence diagram markdown.</returns>
     public string GenerateSequenceDiagram(SqlBreakdownBase sqlBreakdown, string? title = null)
     {
-        return _baseGenerator.GenerateSequenceDiagram(sqlBreakdown, title);
+        return SqlServer.SqlStatementGenerator.GenerateSequenceDiagram(sqlBreakdown, title);
     }
 
     /// <summary>
@@ -37,6 +37,6 @@ public class SqlStatementGenerator
     /// <returns>A string containing the Mermaid ER diagram markdown.</returns>
     public string GenerateEntityRelationshipDiagram(IEnumerable<string> tables, string? title = null)
     {
-        return _baseGenerator.GenerateEntityRelationshipDiagram(tables, title);
+        return SqlServer.SqlStatementGenerator.GenerateEntityRelationshipDiagram(tables, title);
     }
 }

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

@@ -28,6 +28,6 @@ public class QueryBreakdownGenerator
     {
         // Since Snowflake.QueryBreakdown inherits from SqlServer.QueryBreakdown,
         // we can use the base generator which works with the shared properties
-        return _baseGenerator.GenerateMermaidDiagram(queryBreakdown, title);
+        return SqlServer.QueryBreakdownGenerator.GenerateMermaidDiagram(queryBreakdown, title);
     }
 }

src/Strata.SqlTools.Markdown/Snowflake/SqlStatementGenerator.cs

@@ -26,7 +26,7 @@ public class SqlStatementGenerator
     /// <returns>A string containing the Mermaid sequence diagram markdown.</returns>
     public string GenerateSequenceDiagram(SqlBreakdownBase sqlBreakdown, string? title = null)
     {
-        return _baseGenerator.GenerateSequenceDiagram(sqlBreakdown, title);
+        return SqlServer.SqlStatementGenerator.GenerateSequenceDiagram(sqlBreakdown, title);
     }
 
     /// <summary>
@@ -37,6 +37,6 @@ public class SqlStatementGenerator
     /// <returns>A string containing the Mermaid ER diagram markdown.</returns>
     public string GenerateEntityRelationshipDiagram(IEnumerable<string> tables, string? title = null)
     {
-        return _baseGenerator.GenerateEntityRelationshipDiagram(tables, title);
+        return SqlServer.SqlStatementGenerator.GenerateEntityRelationshipDiagram(tables, title);
     }
 }

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

@@ -16,7 +16,7 @@ public class QueryBreakdownGenerator
     /// <param name="queryBreakdown">The QueryBreakdown to visualize.</param>
     /// <param name="title">Optional title for the diagram.</param>
     /// <returns>A string containing the Mermaid markdown diagram.</returns>
-    public string GenerateMermaidDiagram(QueryBreakdown queryBreakdown, string? title = null)
+    public static string GenerateMermaidDiagram(QueryBreakdown queryBreakdown, string? title = null)
     {
         var sb = new StringBuilder();
 

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

@@ -14,7 +14,7 @@ public class SqlStatementGenerator
     /// <param name="sqlBreakdown">The SQL breakdown to visualize.</param>
     /// <param name="title">Optional title for the diagram.</param>
     /// <returns>A string containing the Mermaid markdown sequence diagram.</returns>
-    public string GenerateSequenceDiagram(ISqlBreakdown sqlBreakdown, string? title = null)
+    public static string GenerateSequenceDiagram(ISqlBreakdown sqlBreakdown, string? title = null)
     {
         var sb = new StringBuilder();
 
@@ -74,7 +74,7 @@ public class SqlStatementGenerator
     /// <param name="tableNames">List of table names referenced in the query.</param>
     /// <param name="title">Optional title for the diagram.</param>
     /// <returns>A string containing the Mermaid markdown ER diagram.</returns>
-    public string GenerateEntityRelationshipDiagram(IEnumerable<string> tableNames, string? title = null)
+    public static string GenerateEntityRelationshipDiagram(IEnumerable<string> tableNames, string? title = null)
     {
         var sb = new StringBuilder();