feat: three nuxt frontends, demo seed, rounding + money-exponent + rate-cast fixes, archived specs

apps/api/src/money.rs

@@ -1,5 +1,5 @@
 use rust_decimal::prelude::*;
-use rust_decimal::Decimal;
+use rust_decimal::{Decimal, RoundingStrategy};
 
 use crate::error::ApiError;
 use crate::models::Currency;
@@ -16,7 +16,8 @@ pub fn convert_minor(amount_minor: i64, from: &Currency, to: &Currency) -> Resul
     let to_scale = Decimal::from(10i64.pow(to.exponent as u32));
     // minor(from) -> major(from) -> major(base) -> minor(to)
     let base_major = amount / from_scale / from.rate_to_base;
-    let target = (base_major * to.rate_to_base * to_scale).round_dp(0);
+    let target = (base_major * to.rate_to_base * to_scale)
+        .round_dp_with_strategy(0, RoundingStrategy::MidpointAwayFromZero);
     target
         .to_i64()
         .ok_or_else(|| ApiError::BadRequest("amount out of range".into()))

apps/api/tests/catalog.rs

@@ -146,6 +146,15 @@ async fn currency_conversion_math() {
     assert_eq!(body["amount_minor"], 1500);
     assert_eq!(body["currency"], "JPY");
 
+    // midpoint rounds half-up (away from zero), not banker's rounding:
+    // 1999 minor USD ($19.99) -> JPY at rate 150 => 2998.5 -> 2999
+    let res = client()
+        .get(app.url("/api/currencies/convert?amount_minor=1999&from=USD&to=JPY"))
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(res.json::<serde_json::Value>().await.unwrap()["amount_minor"], 2999);
+
     // disabled currency rejected
     let admin = login_admin(&app).await;
     let res = client()