refactor: 修改分享逻辑和还原旧页面

- 在 app.config.js 中注册 PosterCheckinDetail 页面
- 修改 ActivitiesCover 分享海报逻辑跳转到新页面
- 修改 ActivitiesDetail 分享海报逻辑跳转到新页面
- 还原 PosterCheckin 到旧接口（map.js）

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

@@ -36,6 +36,7 @@ export default {
     'pages/UploadMedia/index',
     'pages/FamilyRank/index',
     'pages/PosterCheckin/index',
+    'pages/PosterCheckinDetail/index',
     'pages/CheckinList/index',
     'pages/CheckinMap/index',
     'pages/JoinOrganization/index',

@@ -629,7 +629,7 @@ defineExpose({
 const onSharePoster = () => {
   console.log('分享海报')
   Taro.navigateTo({
-    url: '/pages/PosterCheckin/index',
+    url: '/pages/PosterCheckinDetail/index',
   })
 }
 

@@ -634,7 +634,7 @@ defineExpose({
 const onSharePoster = () => {
   console.log('分享海报')
   Taro.navigateTo({
-    url: '/pages/PosterCheckin/index',
+    url: '/pages/PosterCheckinDetail/index',
   })
 }