UI: 预览环境显示构建时间 + 售价默认299

- 预览栏显示部署时间（如 04/11 10:05）
- 售价默认299
- vite构建时注入__BUILD_TIME__

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/App.vue

@@ -1,6 +1,6 @@
 <template>
   <div v-if="isPreview" style="background:#e65100;color:white;text-align:center;padding:6px 16px;font-size:13px;font-weight:600;letter-spacing:0.5px;position:sticky;top:0;z-index:100">
-    ⚠️ 预览环境 · PR #{{ prId }} · 数据为生产副本，修改不影响正式环境
+    ⚠️ 预览环境 · PR #{{ prId }} · 数据为生产副本，修改不影响正式环境 · {{ buildInfo }}
   </div>
   <div class="app-header">
     <div class="header-inner">
@@ -116,6 +116,7 @@ const hostname = window.location.hostname
 const prMatch = hostname.match(/^pr-(\d+)\./)
 const isPreview = !!prMatch
 const prId = prMatch ? prMatch[1] : ''
+const buildInfo = __BUILD_TIME__ || ''
 
 function handleTabClick(tab) {
   if (tab.require === 'login' && !auth.isLoggedIn) {

frontend/src/views/Projects.vue

@@ -304,7 +304,7 @@ function selectDemoProject() {
     packaging_cost: p.packaging_cost || 0,
     labor_cost: p.labor_cost || 0,
     other_cost: p.other_cost || 0,
-    selling_price: p.selling_price || 0,
+    selling_price: p.selling_price || 299,
     quantity: p.quantity || 1,
     notes: p.notes || '',
   }
@@ -330,7 +330,7 @@ async function createProject() {
         packaging_cost: 0,
         labor_cost: 0,
         other_cost: 0,
-        selling_price: 0,
+        selling_price: 299,
         quantity: 1,
         notes: '',
       }),
@@ -357,7 +357,7 @@ function selectProject(p) {
     packaging_cost: p.packaging_cost || 0,
     labor_cost: p.labor_cost || 0,
     other_cost: p.other_cost || 0,
-    selling_price: p.selling_price || 0,
+    selling_price: p.selling_price || 299,
     quantity: p.quantity || 1,
     notes: p.notes || '',
   }

frontend/vite.config.js

@@ -1,7 +1,12 @@
 import { defineConfig } from 'vite'
 import vue from '@vitejs/plugin-vue'
 
+const buildTime = new Date().toLocaleString('zh-CN', { timeZone: 'Asia/Shanghai', month: '2-digit', day: '2-digit', hour: '2-digit', minute: '2-digit' })
+
 export default defineConfig({
+  define: {
+    __BUILD_TIME__: JSON.stringify(buildTime),
+  },
   plugins: [vue()],
   server: {
     proxy: {