refactor(domain): move MAX_CENTS to money, deterministic shuffle in tests

fix(domain): guard split allocation and balance invariants

feat(domain): compute net balances and simplified debts

feat(domain): add largest-remainder split allocation

fix(domain): harden schemas, ULID monotonicity and amount parsing

feat(domain): add monotonic ULID generator and money parsing/formatting

feat(domain): add core types and zod schemas