feat:统一前端请求层错误回显与长整型解析

frontend/src/api/json.ts

@@ -0,0 +1,21 @@
+import JSONBig from 'json-bigint';
+
+const jsonParser = JSONBig({
+  storeAsString: true,
+  useNativeBigInt: false,
+});
+
+function looksLikeJsonPayload(data: string) {
+  const trimmed = data.trim();
+  return trimmed.startsWith('{') || trimmed.startsWith('[');
+}
+
+export function parseJsonPreservingLong<T>(data: unknown, contentType?: string): T | unknown {
+  if (typeof data !== 'string' || !looksLikeJsonPayload(data)) {
+    return data;
+  }
+  if (contentType && !contentType.toLowerCase().includes('application/json')) {
+    return data;
+  }
+  return jsonParser.parse(data) as T;
+}