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/app.json

@@ -14,7 +14,9 @@
     "pages/subscribe-plans/subscribe-plans",
     "pages/subscribe-success/subscribe-success",
     "pages/profile/profile",
-    "pages/history/history"
+    "pages/history/history",
+    "pages/help/help",
+    "pages/contact/contact"
   ],
   "window": {
     "navigationBarBackgroundColor": "#ffffff",