Money is integer atomic units, but payout and sum math ran on float64
(`Math.round(base * multiplier)`, `sum + Number(x)`), which silently loses
precision above 2^53 — a real risk for large/credit/XMR amounts.
- Add src/money/atomic.js: the single source of truth for atomic-unit math
(toBig, toSafe, sum, add, mulByDecimal, format). mulByDecimal multiplies an
atomic amount by a decimal multiplier using exact integer arithmetic with
half-up rounding; toSafe narrows to a number only when exactly representable
and otherwise returns a decimal string.
- calculatePayout now uses money.mulByDecimal/toSafe instead of float math.
- walletRPCService batch total + fee sum use money.sum instead of float reduce.
Adds moneyAtomic.test.js with property tests on amounts above 2^53 proving
exactness where the old float path drifted. Full suite: 14 suites / 129 tests.
