feat(api): 构建汇率流水表与定时抓取 API，实现 USD/HKD 对人民币的双点数据入库

src/db/schema.ts

@@ -92,3 +92,15 @@ export const assetPricesHistory = pgTable("asset_prices_history", {
 }, (table) => [
   uniqueIndex("asset_price_date_idx").on(table.assetId, table.date),
 ]);
+
+export const exchangeRatesHistory = pgTable("exchange_rates_history", {
+  id: uuid("id").primaryKey().$defaultFn(() => crypto.randomUUID()),
+  fromCurrency: varchar("from_currency", { length: 10 }).notNull(),
+  toCurrency: varchar("to_currency", { length: 10 }).notNull(),
+  rate: numeric("rate", { precision: 20, scale: 8 }).notNull(),
+  fetchTime: timestamp("fetch_time", { withTimezone: true, mode: "date" })
+    .notNull(),
+  createdAt: timestamp("created_at", { withTimezone: true, mode: "date" })
+    .defaultNow()
+    .notNull(),
+});