feat(upload): 封面上传支持横版与前端压缩

- 新增 imageCompress 与 imagePresets，上传前按规格高质量等比压缩
- 短剧封面拆分为竖版/横版两个上传位，带建议尺寸提示
- 轮播图、创作者中心封面与分集封面接入压缩与提示

src/styles/business/creator-center.css

@@ -188,6 +188,19 @@
   gap: 10px;
 }
 
+.creator-cover-actions {
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+}
+
+.creator-cover-hint {
+  margin: 0;
+  color: #9a97a8;
+  font-size: 12px;
+  line-height: 1.4;
+}
+
 .creator-cover-preview {
   display: grid;
   place-content: center;