Consolidate MONTH_NAMES, PALETTE, formatCurrency, formatCurrencyShort,
ordinal, and fmt into client/src/utils/formatting.js. Consolidate
CONFIG_KEYS into server/src/constants.js. All consumer files updated
to import from these shared modules. PaycheckView re-exports formatCurrency,
ordinal, and formatPayDate for backward compatibility with existing tests.
Nightshift-Task: dead-code
Nightshift-Ref: https://github.com/marcus/nightshift
