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.wxss

@@ -107,6 +107,11 @@
   color: #999;
 }
 
+.sub-card-inactive {
+  background: #f5f5f5;
+  border: 1px dashed #d9d9d9;
+}
+
 .logout-btn {
   text-align: center;
   color: #ff4d4f;