Get category totals

What your assistant is told

Per-category spend/income breakdown for one calendar month — month is "YYYY-MM", e.g. "2026-06". For each category that had activity returns its expense total and income total in minor units. Use this to answer "where did my money go this month?". Read-only. SINGLE-CURRENCY, like get_monthly_summary: the breakdown covers one currency only — the returned currency names it — and excludedCount is how many of the month's transactions were in another currency (excludedCurrencies lists which). Nothing is converted. Note this is the category split only — for the month's income/expense/net headline use get_monthly_summary.