feat(codegen): P 层闭环 —— 模板生成页面 + 画廊生成面板

- src/codegen.ts:PageDeclaration → definePage 源码(漂亮缩进,语法合法)
- src/render.ts:导出 generatePageSource/starterPageFrom;画廊受控 selected/onSelect
- playground generator.tsx:选布局→填标题→生成→复制/保存到 pages/
- vite 中间件 /__vr-save:浏览器 POST 落盘 pages/(HMR 生效)
- 验证:codegen 产物通过工程 tsc;保存中间件落盘成功;画廊 UI headless 通过

examples/playground/vite.config.ts

@@ -1,7 +1,42 @@
-import { defineConfig } from 'vite'
+import { defineConfig, type Plugin } from 'vite'
 import react from '@vitejs/plugin-react'
+import { writeFileSync, mkdirSync } from 'node:fs'
+import { join, dirname } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+/** P 层闭环的写盘中间件:浏览器 POST 源码 → 落盘 pages/(HMR 自动生效) */
+function savePagePlugin(): Plugin {
+  const root = dirname(fileURLToPath(import.meta.url))
+  return {
+    name: 'vr-save-page',
+    configureServer(server) {
+      server.middlewares.use('/__vr-save', (req, res) => {
+        let body = ''
+        req.on('data', (c) => (body += c))
+        req.on('end', () => {
+          try {
+            const { filename, content } = JSON.parse(body) as { filename: string; content: string }
+            if (!/^[a-z0-9-]+\.tsx?$/.test(filename)) {
+              res.statusCode = 400
+              res.end('bad filename')
+              return
+            }
+            const target = join(root, 'pages', filename)
+            mkdirSync(dirname(target), { recursive: true })
+            writeFileSync(target, content, 'utf8')
+            res.setHeader('Content-Type', 'application/json')
+            res.end(JSON.stringify({ ok: true, path: `pages/${filename}` }))
+          } catch (e) {
+            res.statusCode = 500
+            res.end(JSON.stringify({ ok: false, error: String(e) }))
+          }
+        })
+      })
+    },
+  }
+}
 
 export default defineConfig({
-  plugins: [react()],
+  plugins: [react(), savePagePlugin()],
   server: { port: 5183, open: false },
 })