Add Money (finance)

[vhrcgcom]

Description

Implement Money as a ValueObject in the finance module.

Spec: Decimal amount + CurrencyCode; immutable arithmetic helpers

Implementation checklist

• Create src/finance/money.rs
• Implement ValueObject trait
• Add #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
• Export from src/finance/mod.rs and prelude
• Unit tests: valid input · empty input · invalid format · normalisation
• Doc comment with # Example block
• Update status in ROADMAP.md from ⬜ to ✅

Implementation detail

Input / Output

Money is a composite value object.

	Type
Input	MoneyInput { amount: rust_decimal::Decimal, currency: CurrencyCode }
Output	String — e.g. "10.00 EUR"

Validation

• amount may be any finite Decimal value (negative amounts are allowed — they represent debts).
• currency must already be a valid CurrencyCode (validated on construction of that type).

Extra methods

• amount() -> &rust_decimal::Decimal
• currency() -> &CurrencyCode

Notes

Arithmetic helpers (add, subtract, convert) are out of scope for this type — Money is a validated, immutable record, not a calculator. Use rust_decimal directly on amount() if you need math.

References

• ROADMAP.md
• CONTRIBUTING.md