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/subscribe-plans/subscribe-plans.wxss

@@ -1,3 +1,29 @@
+.current-sub {
+  background: #fff9e6;
+  border: 2rpx solid #DCB982;
+  border-radius: 20rpx;
+  padding: 20rpx 24rpx;
+  margin-bottom: 24rpx;
+}
+
+.current-sub-row {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: 8rpx 0;
+}
+
+.current-sub-label {
+  font-size: 24rpx;
+  color: #666666;
+}
+
+.current-sub-value {
+  font-size: 24rpx;
+  color: #333333;
+  font-weight: 600;
+}
+
 .service-card {
   display: flex;
   align-items: center;