Add landing page, referral system, usage quotas, search API management, and yearly pricing

- Separate workspace landing from login for better UX
- Referral system rewards both parties with Pro days
- Quota enforcement prevents abuse without breaking endpoints
- 7-day free trial with auto-downgrade on expiry
- Admin-managed search provider config (SearXNG, Bing)
- 15% discount on annual subscriptions
- MCP search server wrapping opencode search
- Fix discovery module field name mismatch causing 422

user-frontend/src/views/Translate.vue

@@ -3,7 +3,7 @@
     <el-card shadow="never">
       <template #header><span>文本翻译</span></template>
       <el-input v-model="form.text" type="textarea" :rows="5" placeholder="输入需要翻译的外贸文本..." />
-      <div style="margin:16px 0;display:flex;gap:12px;align-items:center">
+      <div style="margin:16px 0;display:flex;gap:12px;align-items:center;flex-wrap:wrap">
         <el-select v-model="form.target_lang" style="width:160px">
           <el-option label="英语" value="en" />
           <el-option label="中文" value="zh" />