Creates Form1099Boxes and Payee1099s tables; adds Form1099BoxId to
ExpenseSubCategories and ExpenseCategoryGroups; adds PayeeId to
Expenses. All new columns nullable, all FKs with SetNull, unique index
on Form1099Boxes.BoxCode. No data backfill.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Chris Chen