Every section maps to a group. Group order and defaults match the
spec. Budget and month subtotal calculations check out across
seeded entries. Pages render the expected details ids, income is
open by default, committed is closed. Mutations return OOB group
total spans. Sinking Funds section is visible on both pages.
Refs #11
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
