fix(admin): improve promo layout and system settings save UX

Fix mini home media form persistence; float save with unsaved leave prompt; promo detail QR on the right.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/dukang-api/src/common/system-config/system-config.registry.ts

@@ -74,7 +74,7 @@ export const SYSTEM_CONFIG_FIELDS: SystemConfigFieldMeta[] = [
     group: G.wechat_mini,
     type: 'imageList',
     requiresRestart: false,
-    description: '小程序商品首页顶部轮播，建议比例 15:8，最多 8 张',
+    description: '小程序商品首页顶部轮播，建议比例 15:8，最多 8 张；上传后需点击右上角「保存」',
   },
   {
     key: 'MINI_HOME_FOOTER_URL',
@@ -82,7 +82,7 @@ export const SYSTEM_CONFIG_FIELDS: SystemConfigFieldMeta[] = [
     group: G.wechat_mini,
     type: 'image',
     requiresRestart: false,
-    description: '小程序商品首页底部 footer，建议比例 15:4',
+    description: '小程序商品首页底部 footer，建议比例 15:4；上传后需点击右上角「保存」',
   },
 
   { key: 'OSS_ACCESS_KEY_ID', label: 'OSS AccessKey ID', group: G.oss, type: 'password', secret: true, requiresRestart: true },