Set-operation orderBy() ignores casing config (pg + sqlite), producing a non-existent column reference #5987

Description

With casing: 'snake_case' (columns declared without an explicit DB name), ordering a set operation (union/intersect/except/…) by a column emits the JS property name in ORDER BY instead of the cased DB column name. The SELECT list is cased correctly, so ORDER BY references a column that isn't in the result set — the query fails at runtime (Postgres: column "firstName" does not exist). Affects pg (bare and asc()/desc()-wrapped) and sqlite (bare-column path). mysql/singlestore are unaffected.

Steps to reproduce

import { pgTable, text, PgDialect, QueryBuilder } from 'drizzle-orm/pg-core';
import { asc, union } from 'drizzle-orm';

const users = pgTable('users', { firstName: text() }); // no explicit db name
const dialect = new PgDialect({ casing: 'snake_case' });
const qb = new QueryBuilder(dialect);

union(qb.select().from(users), qb.select().from(users)).orderBy(asc(users.firstName));

Generated SQL:

observed: (select "first_name" from "users") union (select "first_name" from "users") order by "firstName" asc
expected: (select "first_name" from "users") union (select "first_name" from "users") order by "first_name" asc

A plain select().orderBy(asc(users.firstName)) is correct (order by "users"."first_name" asc); only set-operation ordering is affected.

Root cause

buildSetOperationQuery emits the raw column .name instead of casing.getColumnCasing(...):

• drizzle-orm/src/pg-core/dialect.ts:483 (bare column) and :489 (sql-wrapped chunk)
• drizzle-orm/src/sqlite-core/dialect.ts:478 (bare column)

The correct pattern is already used in mysql-core/dialect.ts:528,536, singlestore-core/dialect.ts, and sqlite-core/dialect.ts:485.

Suggested fix

Replace those three sites with this.casing.getColumnCasing(<column>) (the column object, matching mysql). After the change, all set-operation ORDER BY clauses emit "first_name", and plain selects are unchanged.