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

2026-09-17 13:34:38 +08:00
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+# currency Specification
+
+## Purpose
+TBD - created by archiving change catalog-i18n-currency. Update Purpose after archive.
+## Requirements
+### Requirement: Currency registry
+The system SHALL maintain a currencies table: ISO code, localized name, symbol, exponent (minor units), enabled flag, and `rate_to_base` (NUMERIC). Exactly one currency is the base.
+
+#### Scenario: seeded currencies
+- **WHEN** migrations finish
+- **THEN** USD exists as base with rate 1, and CNY/EUR/JPY exist with positive rates
+
+### Requirement: Amount conversion
+`GET /api/currencies/convert` SHALL convert integer minor units between enabled currencies via base rates, rounding half-up to the target exponent.
+
+#### Scenario: USD to JPY
+- **WHEN** converting 1000 minor USD (=$10.00) to JPY with rate 150
+- **THEN** the result is 1500 minor JPY (¥1500), an integer
+
+#### Scenario: disabled currency rejected
+- **WHEN** converting to a disabled or unknown currency
+- **THEN** the API returns 400
+