implement exchange settings management and fallback rate handling

packages/api-common/src/services/exchange/exchange.service.ts

@@ -1,6 +1,6 @@
 import { Inject, Injectable } from "@nestjs/common";
 
-import { CbeExchangeProvider } from "./cbe.provider";
+import { CbeExchangeProvider, CbeProviderStatus } from "./cbe.provider";
 import { EXCHANGE_OPTIONS, ExchangeOptions } from "./exchange.options";
 import { CurrencyCode } from "./exchange.types";
 
@@ -47,6 +47,14 @@ export class ExchangeService {
     );
   }
 
+  /**
+   * Health of the underlying rate feed — what was served last and whether it
+   * is currently failing. For operator-facing status displays.
+   */
+  getProviderStatus(): CbeProviderStatus {
+    return this.provider.getStatus();
+  }
+
   /** Converts `amount` from one currency to another using {@link getRate}. */
   async convert(
     amount: number,