feat: show trial plan with used/disabled state on subscribe page

- Add GET /api/v1/subscription/plans public endpoint for pricing
- Subscription API now returns trial_used field
- Subscribe-plans page shows trial card, greyed out with "已使用" tag
  when trial has been used
- Trial activation calls dedicated trial API, not purchase
- Prices fetched from server settings, fallback to defaults

miniprogram/pages/subscribe-plans/subscribe-plans.js

@@ -32,33 +32,52 @@ Page({
   loadPlans: function () {
     var self = this
     api.getPlans().then(function (data) {
-      var plans = (data.plans || []).filter(function (p) { return p.key !== 'trial' }).map(function (p) {
+      var serverPlans = data.plans || []
+      var monthlyPrice = 99
+      for (var i = 0; i < serverPlans.length; i++) {
+        if (serverPlans[i].key === 'monthly') monthlyPrice = serverPlans[i].price
+      }
+      var plans = serverPlans.map(function (p) {
         var daily = p.days > 0 ? (p.price / p.days).toFixed(1) : 0
+        var desc = ''
+        if (p.key === 'trial') desc = p.days + '天免费体验'
+        else if (p.key === 'yearly') desc = '省¥' + Math.round(monthlyPrice * 12 - p.price)
+        else desc = '约' + daily + '元/天'
         return {
           key: p.key,
           name: p.name,
           price: p.price,
-          priceLabel: '¥' + p.price,
-          desc: p.key === 'yearly' ? '省¥' + ((p.price / 12 * 12) > 0 ? Math.round(self._monthlyPrice(data.plans) * 12 - p.price) : '') : '约' + daily + '元/天',
-          tag: p.key === 'yearly' ? '推荐' : ''
+          priceLabel: p.key === 'trial' ? '免费' : '¥' + p.price,
+          desc: desc,
+          tag: p.key === 'yearly' ? '推荐' : '',
+          disabled: false
         }
       })
       if (plans.length > 0) self.setData({ plans: plans })
+      self.checkTrialUsed()
     }).catch(function () {
       self.setData({
         plans: [
+          { key: 'trial', name: '试用', price: 0, priceLabel: '免费', desc: '7天免费体验', disabled: false },
           { key: 'monthly', name: '月卡', price: 99, priceLabel: '¥99', desc: '约3.3元/天' },
           { key: 'yearly', name: '年卡', price: 899, priceLabel: '¥899', desc: '省¥289', tag: '推荐' }
         ]
       })
+      self.checkTrialUsed()
     })
   },
 
-  _monthlyPrice: function (plans) {
-    for (var i = 0; i < plans.length; i++) {
-      if (plans[i].key === 'monthly') return plans[i].price
+  checkTrialUsed: function () {
+    var self = this
+    var sub = self.data.subscription
+    if (sub && sub.trial_used) {
+      var plans = self.data.plans.map(function (p) {
+        if (p.key === 'trial') return Object.assign({}, p, { disabled: true, tag: '已使用' })
+        return p
+      })
+      self.setData({ plans: plans })
+      if (self.data.selected === 'trial') self.setData({ selected: 'yearly' })
     }
-    return 99
   },
 
   loadSubscription: function () {
@@ -68,6 +87,7 @@ Page({
         subscription: sub,
         subRemaining: sub.remaining_days || 0
       })
+      self.checkTrialUsed()
     }).catch(function () {})
   },
 
@@ -85,7 +105,18 @@ Page({
         break
       }
     }
-    if (!plan) return
+    if (!plan || plan.disabled) return
+
+    if (plan.key === 'trial') {
+      wx.showModal({
+        title: '激活试用',
+        content: '免费试用 ' + plan.desc + '？',
+        success: function (res) {
+          if (res.confirm) self.doActivateTrial()
+        }
+      })
+      return
+    }
 
     wx.showModal({
       title: '确认支付',
@@ -98,6 +129,21 @@ Page({
     })
   },
 
+  doActivateTrial: function () {
+    var self = this
+    self.setData({ purchasing: true })
+    api.activateTrial().then(function () {
+      self.setData({ purchasing: false })
+      wx.showToast({ title: '试用已激活', icon: 'success' })
+      setTimeout(function () {
+        wx.redirectTo({ url: '/pages/subscribe-success/subscribe-success?plan=trial' })
+      }, 1000)
+    }).catch(function (err) {
+      self.setData({ purchasing: false })
+      wx.showToast({ title: err.message || '激活失败', icon: 'none' })
+    })
+  },
+
   doPurchase: function (plan) {
     var self = this
     self.setData({ purchasing: true })

miniprogram/pages/subscribe-plans/subscribe-plans.wxml

@@ -29,8 +29,8 @@
     </view>
 
     <view class="plans">
-      <view class="plan {{selected === item.key ? 'selected' : ''}}" wx:for="{{plans}}" wx:key="key" bindtap="onSelect" data-plan="{{item.key}}">
-        <view class="plan-tag {{selected === item.key ? 'plan-tag-active' : ''}}" wx:if="{{item.tag}}">{{item.tag}}</view>
+      <view class="plan {{selected === item.key ? 'selected' : ''}} {{item.disabled ? 'plan-disabled' : ''}}" wx:for="{{plans}}" wx:key="key" bindtap="{{item.disabled ? '' : 'onSelect'}}" data-plan="{{item.key}}">
+        <view class="plan-tag {{item.disabled ? 'plan-tag-disabled' : (selected === item.key ? 'plan-tag-active' : '')}}" wx:if="{{item.tag}}">{{item.tag}}</view>
         <view class="plan-price">{{item.priceLabel}}</view>
         <view class="plan-name">{{item.name}}</view>
         <view class="plan-save">{{item.desc}}</view>

miniprogram/pages/subscribe-plans/subscribe-plans.wxss

@@ -118,3 +118,13 @@
 .btn-primary-gold::after {
   border: none;
 }
+
+.plan-disabled {
+  opacity: 0.5;
+  pointer-events: none;
+}
+
+.plan-tag-disabled {
+  background: #ccc;
+  color: #fff;
+}