Track statement and transaction balance history

[codeforester]

Summary

Capture the future balance-history model for BankBuddy after the first ICICI spreadsheet import establishes account-level latest balance snapshots.

Context

The ICICI .xls export includes row balances. The first importer should use those balances for import sanity checks and update account-level latest balance fields, but it should not store every row balance unless we need a historical ledger view.

Future Design Questions

• Add statement_balances for opening/closing balance snapshots per imported statement/account/source file?
• Add transaction_balances or balance_after_minor_units only if we need per-row ledger reconstruction?
• How should balance history interact with re-imports, duplicate files, and corrected statements?
• How should CLI reports expose historical balances without implying live bank connectivity?

Initial Recommendation

Prefer statement_balances before transaction_balances. Keep account-level latest balance fields as the current snapshot, sourced from the latest successfully imported statement.

Acceptance Criteria

• Document the balance-history schema decision.
• Add migrations and import/update behavior if the design chooses persistence.
• Include reconciliation tests around opening/closing balances and row balances where available.