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.js

@@ -60,22 +60,21 @@ Page({
   },
 
   onViewSubscription: function () {
-    if (!this.data.subscription || this.data.subscription.status !== 'active') {
-      wx.navigateTo({ url: '/pages/subscribe-plans/subscribe-plans' })
-    } else {
-      var sub = this.data.subscription
-      wx.showModal({
-        title: '订阅信息',
-        content: '套餐类型：' + (sub.plan || '未知') + '\n剩余天数：' + (sub.remaining_days || 0) + '天',
-        showCancel: false
-      })
-    }
+    wx.navigateTo({ url: '/pages/subscribe-plans/subscribe-plans' })
   },
 
   onViewHistory: function () {
     wx.switchTab({ url: '/pages/history/history' })
   },
 
+  onHelp: function () {
+    wx.navigateTo({ url: '/pages/help/help' })
+  },
+
+  onContact: function () {
+    wx.navigateTo({ url: '/pages/contact/contact' })
+  },
+
   onLogout: function () {
     wx.showModal({
       title: '退出登录',