Follow-up to T3 (Decimal migration): display layer still hardcodes :,.2f
everywhere, which is wrong for JPY (0 dp) and 3-dp currencies like BHD/KWD/OMR.
T8 = display-only refactor:
- CURRENCY_DECIMALS + CurrencyConverter.format_money() in domain/
- replace 14 :,.2f literals across infrastructure/cli/
- rework 2 i18n templates that bake the format into the message string
- extend tests/test_currency.py with JPY/BHD/USD/CHF cases
Locked decisions (HALF_UP, ',' separator, suffix for unknown codes,
internal precision untouched) recorded in req-T8.json for the executing node.
