Ship signup sheet, subscribe reminders, cover crop, and theme updates.

Wire real WeChat app config, prefer activity cover over posters, and add admin cover cropping for the home banner.

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

miniprogram/pages/signup/signup.wxml

@@ -1,12 +1,6 @@
-<view class="page">
-  <view class="card">
-    <text class="label">姓名</text>
-    <input class="input" placeholder="怎么称呼你" placeholder-class="placeholder" value="{{name}}" maxlength="20" bindinput="onName" />
-    <text class="label">手机号</text>
-    <input class="input" type="number" placeholder="用于活动通知" placeholder-class="placeholder" value="{{phone}}" maxlength="11" bindinput="onPhone" />
-    <text class="label">公司 / 机构</text>
-    <input class="input" placeholder="选填" placeholder-class="placeholder" value="{{company}}" maxlength="40" bindinput="onCompany" />
-  </view>
-  <view class="save {{submitting ? 'busy' : ''}}" bindtap="submit">{{submitting ? '提交中…' : '提交报名'}}</view>
-  <text class="hint">手机号仅用于本次活动通知。</text>
-</view>
+<signup-sheet
+  show="{{true}}"
+  activity-id="{{activityId}}"
+  bind:close="onClose"
+  bind:success="onSuccess"
+/>