Translate every Italian /// XML doc comment, <!-- --> XAML comment, and
// inline comment to English across all source files (Core, App, tests).
Add the language policy to CLAUDE.md (conversation Italian; all code
and docs English). Update one test assertion that checked an Italian
exception message that was also translated.
Replace the silent (long) cast with an explicit fractional check:
if value * factor has a non-zero remainder, TryParseIn/TryParseCoins
return false. The caller already shows "Importo non valido." to the
user, so no UI change is needed.
Covers TryParseIn (all units) and TryParseCoins. Adds CoinAmountTests
with valid and invalid cases including the triggering example (1.9 sat).