统一客户端维护态错误弹窗

客户端维护响应统一识别并广播维护事件

AGC 与网页端根部展示维护大弹窗，收口发布、上传、资源换签和登录错误

补充维护态弹窗测试、类型检查与实施计划说明

src/services/apiClient.ts

@@ -12,6 +12,7 @@ import { getHostRuntime } from './host-bridge/hostBridge';
 
 const ACCESS_TOKEN_KEY = 'genarrative.auth.access-token.v1';
 export const AUTH_STATE_EVENT = 'genarrative-auth-state-changed';
+export const MAINTENANCE_EVENT = 'genarrative-maintenance-detected';
 const REQUEST_ID_HEADER = 'x-request-id';
 const API_VERSION_HEADER = 'x-api-version';
 const ROUTE_VERSION_HEADER = 'x-route-version';
@@ -505,6 +506,38 @@ function shouldRetryResponse(
   );
 }
 
+export function isMaintenanceApiError(error: unknown) {
+  return (
+    error instanceof ApiClientError &&
+    (error.code.trim().toUpperCase() === 'MAINTENANCE' ||
+      (error.status === 503 && error.message.includes('维护')))
+  );
+}
+
+export function emitMaintenanceNotice(error?: unknown) {
+  if (typeof globalThis.dispatchEvent !== 'function') {
+    return;
+  }
+
+  if (error !== undefined && !isMaintenanceApiError(error)) {
+    return;
+  }
+
+  const detail =
+    error instanceof ApiClientError
+      ? {
+          code: error.code,
+          status: error.status,
+          requestId: error.meta.requestId,
+        }
+      : undefined;
+  const event =
+    typeof CustomEvent === 'function'
+      ? new CustomEvent(MAINTENANCE_EVENT, { detail })
+      : new Event(MAINTENANCE_EVENT);
+  globalThis.dispatchEvent(event);
+}
+
 export function isAbortError(error: unknown) {
   return (
     error instanceof Error &&
@@ -1001,7 +1034,7 @@ async function buildApiClientError(
     undefined;
   const baseMessage = parseApiErrorMessage(responseText, fallbackMessage);
 
-  return new ApiClientError({
+  const error = new ApiClientError({
     message: requestId
       ? `${baseMessage}（requestId: ${requestId}）`
       : baseMessage,
@@ -1024,6 +1057,10 @@ async function buildApiClientError(
     },
     responseText,
   });
+  if (isMaintenanceApiError(error)) {
+    emitMaintenanceNotice(error);
+  }
+  return error;
 }
 
 export async function requestJson<T>(