feat: registration gravity from DB config instead of hardcoded

- Add registrationGravity to pricing config (default 50, adjustable via admin)
- Inject PricingService into UserService, read config for all 4 registration paths
- Expose registrationGravity in /member/plans response for frontend
- Login page fetches dynamic value from API, replaces hardcoded '50'
- Update user.vue gravity card copy

zhiyin-app/src/pages/login/login.vue

@@ -65,6 +65,13 @@
       <view class="card" v-if="mainTab === 'register'">
         <text class="card-title">创建账号</text>
         <text class="card-sub">注册后享受 AI 面试模拟服务</text>
+        <view class="promo-banner">
+          <text class="promo-icon">🎁</text>
+          <view class="promo-texts">
+            <text class="promo-title">注册即送 {{ registrationGravity }} 引力值</text>
+            <text class="promo-desc">免费体验 AI 面试模拟</text>
+          </view>
+        </view>
         <view class="field">
           <text class="field-label">邮箱</text>
           <input class="input" type="text" v-model="email" placeholder="请输入邮箱" />
@@ -133,6 +140,7 @@ const agreed = ref(false)
 const mainTab = ref('login')
 const loginMode = ref('password') // 'password' | 'code'
 const isMp = ref(false)
+const registrationGravity = ref(50)
 
 const email = ref('')
 const password = ref('')
@@ -158,6 +166,17 @@ onMounted(() => {
   isMp.value = true
   mainTab.value = 'wechat'
   // #endif
+  // 获取注册赠送引力值配置
+  uni.request({
+    url: api('/member/plans'),
+    method: 'GET',
+    success: (res) => {
+      if (res.statusCode === 200 && res.data?.registrationGravity) {
+        registrationGravity.value = res.data.registrationGravity
+      }
+    },
+    fail: () => {} // 使用默认值 50
+  })
 })
 
 onBeforeUnmount(() => { if (timer) { clearTimeout(timer); timer = null } })
@@ -355,6 +374,12 @@ const goPrivacy = () => uni.navigateTo({ url: '/pages/privacy/privacy' })
 .card-title { font-size: 30rpx; font-weight: 700; color: var(--color-text); display: block; }
 .card-sub { font-size: 22rpx; color: var(--color-text-tertiary); margin-top: 6rpx; margin-bottom: 24rpx; display: block; }
 
+/* ===== Promo Banner ===== */
+.promo-banner { background: linear-gradient(135deg, #FEF3C7, #FDE68A); border-radius: var(--radius-md); padding: 20rpx 24rpx; margin-bottom: 24rpx; display: flex; align-items: center; gap: 16rpx; }
+.promo-icon { font-size: 36rpx; }
+.promo-title { font-size: 26rpx; font-weight: 700; color: #92400E; display: block; }
+.promo-desc { font-size: 22rpx; color: #B45309; display: block; margin-top: 4rpx; }
+
 /* ===== Fields ===== */
 .field { margin-bottom: 20rpx; }
 .field-label { font-size: 22rpx; color: var(--color-text-secondary); margin-bottom: 8rpx; display: block; }