fix(gosqlx): ExtractColumns reports SELECT aliases referenced in ORDER BY/HAVING as columns #849

Summary

gosqlx.ExtractColumns and gosqlx.ExtractColumnsQualified report a SELECT-list alias as a column whenever the alias is referenced in ORDER BY or HAVING. The alias is an output name, not a column of any table.

Users see this in the MCP extract_metadata / analyze_sql tools and in the ChatGPT widget. In a live ChatGPT test, ORDER BY orders listed orders under Columns.

Reproduction (main @ f0ebf86)

tree, _ := gosqlx.Parse(sql)
gosqlx.ExtractColumns(tree)
gosqlx.ExtractColumnsQualified(tree)

The qualified variant has the same problem. For the first query it returns orders unqualified next to o.id o.user_id u.id.

Expected behaviour

An unqualified identifier in ORDER BY (and HAVING, which MySQL and others allow to use aliases) that matches a SELECT-list alias in the same query block should resolve to that alias and be left out of the column list.

Keep reporting the identifier as a column when:

• it is qualified (t.total);
• no alias in the same SELECT has that name.

Aliases from outer or inner query blocks (subqueries, CTEs) should not suppress columns in another block.

Notes

• This lives in pkg/gosqlx/extract.go (column collector), not in the parser.
• Add table-driven cases to pkg/gosqlx/extract_test.go, including a negative case where a real column shares a name with an alias defined in a subquery.
• Found while testing the GoSQLX ChatGPT app (feat: GoSQLX Claude Code plugin and ChatGPT app #823).