feat(admin): enrich admin panel fields; add user index constraint and customer service

- admin controller: add updatedAt to interview/resume selects; add orderCount,
  todayOrders, totalRevenue to overview
- admin.vue: enrich all tabs with more fields
  - overview: order cards (count, revenue)
  - users: wxOpenid, email, createdAt, interviewCount, vipExpireAt, role badge
  - interviews: user email, updatedAt, summary preview
  - orders: title, type, channel, paidAt, wxTransactionId, refund info
  - resumes: user email, updatedAt
  - share: sharer phone, shareCode, isActive, visitorId(IP), creditedAt
  - admins: email, createdAt
- user.schema: add unique indexes on phone/wxOpenid/email; pre-save hook
  requiring at least one contact method
- user/about: add WeChat contact button (open-type=contact) for customer service

zhiyin-app/src/pages/user/user.vue

@@ -97,6 +97,13 @@
         </view>
       </view>
       <view class="menu-group">
+        <!-- #ifdef MP-WEIXIN -->
+        <button class="menu-item contact-btn" open-type="contact">
+          <view class="menu-icon-wrap wrap-gray"><text class="menu-icon">💬</text></view>
+          <text class="menu-text">联系客服</text>
+          <text class="menu-arrow">›</text>
+        </button>
+        <!-- #endif -->
         <view class="menu-item" @click="goAbout">
           <view class="menu-icon-wrap wrap-gray"><text class="menu-icon">ℹ️</text></view>
           <text class="menu-text">关于</text>
@@ -322,6 +329,9 @@ const doLogout = () => {
 .menu-area { padding: 0 32rpx 32rpx; margin-top: 8rpx; }
 .menu-group { background: #FFFFFF; border-radius: var(--radius-lg); overflow: hidden; margin-bottom: 24rpx; box-shadow: var(--shadow-sm); }
 .menu-item { display: flex; align-items: center; padding: 28rpx 32rpx; border-bottom: 1rpx solid var(--color-border); }
+.contact-btn { width: 100%; background: transparent; border: none; border-radius: 0; padding: 0; margin: 0; line-height: inherit; font-size: inherit; text-align: left; }
+.contact-btn::after { border: none; }
+.contact-btn:active { background: #F9FAFB; }
 .menu-item:last-child { border-bottom: none; }
 .menu-item:active { background: #F9FAFB; }
 .menu-icon-wrap { width: 60rpx; height: 60rpx; border-radius: var(--radius-md); display: flex; align-items: center; justify-content: center; margin-right: 20rpx; flex-shrink: 0; }