fix: resolve subscription UX issues and add placeholder pages

- Profile: show "未订阅" card when subscription inactive/0 days
- Profile: subscription management navigates to page instead of modal
- Subscribe-plans: data-driven plan cards with mock payment flow
- Subscribe-plans: show current subscription status at top
- Subscribe-prompt: "先使用普通模式" goes to wear-check directly
- Add help and contact placeholder pages
- Fix unbindDevice to work without explicit deviceId

miniprogram/pages/profile/profile.wxml

@@ -8,12 +8,19 @@
       </view>
     </view>
 
-    <view class="sub-card" wx:if="{{subscription}}">
+    <view class="sub-card" wx:if="{{subscription && subscription.status === 'active' && subRemaining > 0}}">
       <view class="sub-left">
         <view class="sub-name">✨ 智能模式</view>
         <view class="sub-remain">剩余 {{subRemaining}}天</view>
       </view>
-      <text class="status-badge status-badge-gold">试用中</text>
+      <text class="status-badge status-badge-gold">使用中</text>
+    </view>
+    <view class="sub-card sub-card-inactive" wx:else bindtap="onViewSubscription">
+      <view class="sub-left">
+        <view class="sub-name">智能模式</view>
+        <view class="sub-remain">未订阅</view>
+      </view>
+      <text class="status-badge" style="background:#eee;color:#999;">去订阅 ›</text>
     </view>
 
     <view class="menu-list">
@@ -34,12 +41,12 @@
         <view class="menu-text">订阅管理</view>
         <text class="menu-arrow">›</text>
       </view>
-      <view class="menu-item">
+      <view class="menu-item" bindtap="onHelp">
         <view class="menu-icon">❓</view>
         <view class="menu-text">使用帮助</view>
         <text class="menu-arrow">›</text>
       </view>
-      <view class="menu-item">
+      <view class="menu-item" bindtap="onContact">
         <view class="menu-icon">📞</view>
         <view class="menu-text">联系我们</view>
         <text class="menu-arrow">›</text>