发布封面导入器收敛为单选

- 新增 COVER_IMPORTER_SETTINGS（maxItems: 1），FormCard 封面导入改用该设置，避免多选后静默丢弃其余图片

apps/ai-game-creator-shell/src/components/AssetImporter/settings.ts

@@ -127,6 +127,16 @@ export const DESIGN_IMAGE_IMPORTER_SETTINGS: AssetImporterSettings =
 export const SPRITE_IMPORTER_SETTINGS: AssetImporterSettings =
   imageImporterSettings(imageRequirements);
 
+/**
+ * 单张封面：发布表单的封面槽只装一个路径，导入器同样收敛成单选；沿用多选的
+ * `SPRITE_IMPORTER_SETTINGS` 时用户多选的其余图片会被静默丢弃。
+ */
+export const COVER_IMPORTER_SETTINGS: AssetImporterSettings =
+  imageImporterSettings({
+    maxItems: 1,
+    maxFileSizeBytes: 20 * 1024 * 1024,
+  });
+
 /**
  * 平台图标（小红书小工具等）：本地项目与云端素材库两个来源都要能选，单张、png/jpg/jpeg、≤5 MiB。
  * 上限与白名单跟宿主 `validate_icon` 对齐，免得选完了保存时才被宿主的硬校验挡回来。

apps/ai-game-creator-shell/src/view/project-development/export/tabs/taonier/FormCard.tsx

@@ -2,7 +2,10 @@ import { ImagePlus, Sparkles, Trash2 } from 'lucide-react';
 import { type ReactNode, useState } from 'react';
 
 import { AssetImporter } from '../../../../../components/AssetImporter';
-import { SPRITE_IMPORTER_SETTINGS } from '../../../../../components/AssetImporter/settings';
+import {
+  COVER_IMPORTER_SETTINGS,
+  SPRITE_IMPORTER_SETTINGS,
+} from '../../../../../components/AssetImporter/settings';
 import { MAX_AGC_GAME_SCREENSHOTS } from '../../../../../services/gameDistributionPublish';
 import type { TaonierExportForm } from '../../generated/TaonierExportForm';
 import {
@@ -382,7 +385,7 @@ export function FormCard({
       <AssetImporter
         open={coverImporterOpen}
         projectPath={projectPath ?? ''}
-        settings={SPRITE_IMPORTER_SETTINGS}
+        settings={COVER_IMPORTER_SETTINGS}
         onClose={() => setCoverImporterOpen(false)}
         onImport={(assets) => {
           const picked = assets.at(-1);