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.service.ts

@@ -5,7 +5,7 @@ import type {
   SystemConfigSyncResult,
   SystemConfigUpdateRequest,
 } from '@dukang/shared-types';
-import { loadAppConfig } from '@dukang/shared-types';
+import { loadAppConfig, parseMiniHomeBanners, serializeMiniHomeBanners } from '@dukang/shared-types';
 import { PrismaService } from '../prisma/prisma.module';
 import {
   SYSTEM_CONFIG_FIELDS,
@@ -209,6 +209,12 @@ export class SystemConfigService implements OnModuleInit {
     if (meta.type === 'boolean') {
       return raw === 'true' || raw === '1' ? 'true' : 'false';
     }
+    if (meta.type === 'imageList') {
+      return serializeMiniHomeBanners(parseMiniHomeBanners(raw));
+    }
+    if (meta.type === 'image') {
+      return raw.trim();
+    }
     if (meta.key === 'WX_MCH_PRIVATE_KEY' || meta.key === 'WX_PLATFORM_CERT') {
       let value = raw.trim();
       if (