feat(ds-flow): Phase 1.1-1.2 — 原型单源目录 + tokens.css 迁为真源

- design/prototype/serve.mjs:零依赖热重载预览服务器(照搬 jiu,check-ds
  存在性守护,Phase 5 前静默跳过)
- design/prototype/tokens.css:token 真源(现结构已满足 ds-flow 的
  base :root + [data-theme=dark],字节迁移保证 codegen 零 diff)
- design/colors_and_type.css:退化为薄 @import 别名(供历史 preview/*.html
  浏览器内引用;codegen 不再读它)
- 三个 codegen(Flutter gen_flutter_tokens / website+usercenter build-tokens)
  + drift 检查全部重指向 prototype/tokens.css
- 生成产物 diff 仅头注释源路径行,token 数值零变化(已验证)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

design/prototype/serve.mjs

@@ -0,0 +1,97 @@
+// 零依赖本地热重载静态服务器 — pangolin 原型单源预览
+// 用法: node design/prototype/serve.mjs [port]   默认 5180
+// 评审给 URL,不截图(ds-flow L3)。
+import http from 'node:http';
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { spawn } from 'node:child_process';
+
+const ROOT = path.dirname(fileURLToPath(import.meta.url));
+const PORT = Number(process.argv[2]) || 5180;
+
+const MIME = {
+  '.html': 'text/html; charset=utf-8',
+  '.css': 'text/css; charset=utf-8',
+  '.js': 'text/javascript; charset=utf-8',
+  '.mjs': 'text/javascript; charset=utf-8',
+  '.json': 'application/json; charset=utf-8',
+  '.svg': 'image/svg+xml',
+  '.png': 'image/png',
+  '.jpg': 'image/jpeg',
+  '.woff2': 'font/woff2',
+  '.otf': 'font/otf',
+  '.ttf': 'font/ttf',
+};
+
+const clients = new Set();
+const RELOAD_SNIPPET = `\n<script>
+(function(){ try{
+  var es=new EventSource('/__reload');
+  es.onmessage=function(){ location.reload(); };
+}catch(e){} })();
+</script>\n`;
+
+const server = http.createServer((req, res) => {
+  if (req.url === '/__reload') {
+    res.writeHead(200, {
+      'Content-Type': 'text/event-stream',
+      'Cache-Control': 'no-cache',
+      Connection: 'keep-alive',
+    });
+    res.write('retry: 500\n\n');
+    clients.add(res);
+    req.on('close', () => clients.delete(res));
+    return;
+  }
+
+  let urlPath = decodeURIComponent(req.url.split('?')[0]);
+  if (urlPath === '/') urlPath = '/index.html';
+  const filePath = path.join(ROOT, urlPath);
+  if (!filePath.startsWith(ROOT)) { res.writeHead(403); res.end('forbidden'); return; }
+
+  fs.readFile(filePath, (err, data) => {
+    if (err) { res.writeHead(404, { 'Content-Type': 'text/html; charset=utf-8' }); res.end('<h1>404</h1>'); return; }
+    const ext = path.extname(filePath).toLowerCase();
+    const mime = MIME[ext] || 'application/octet-stream';
+    const noCache = { 'Cache-Control': 'no-store, no-cache, must-revalidate', 'Pragma': 'no-cache', 'Expires': '0' };
+    if (ext === '.html') {
+      const html = data.toString('utf8').replace('</body>', RELOAD_SNIPPET + '</body>');
+      res.writeHead(200, { 'Content-Type': mime, ...noCache });
+      res.end(html);
+    } else {
+      res.writeHead(200, { 'Content-Type': mime, ...noCache });
+      res.end(data);
+    }
+  });
+});
+
+// 设计系统守门:启动 + 每次改动自动跑 check-ds.mjs(Phase 5 建立后生效)。
+const CHECK_DS = path.join(ROOT, 'tools', 'check-ds.mjs');
+function runDsCheck() {
+  if (!fs.existsSync(CHECK_DS)) return; // Phase 5 前无闸,静默跳过
+  const p = spawn(process.execPath, [CHECK_DS], { cwd: ROOT });
+  let out = '';
+  p.stdout.on('data', d => out += d);
+  p.stderr.on('data', d => out += d);
+  p.on('close', code => {
+    const t = new Date().toLocaleTimeString();
+    if (code === 0) console.log(`\x1b[32m[设计系统 ✓ ${t}] 颜色全部走 token、变量均已定义\x1b[0m`);
+    else console.log(`\x1b[31m[设计系统 ✗ ${t}] 存在违规 —— 运行 node tools/check-ds.mjs 看详情\x1b[0m`);
+  });
+}
+
+let debounce;
+fs.watch(ROOT, { recursive: true }, (_ev, file) => {
+  if (file && file.endsWith('serve.mjs')) return;
+  clearTimeout(debounce);
+  debounce = setTimeout(() => {
+    for (const c of clients) c.write('data: reload\n\n');
+    if (file && /\.(html|css|js)$/.test(file)) runDsCheck();
+  }, 80);
+});
+
+server.listen(PORT, () => {
+  console.log(`prototype live at http://localhost:${PORT}/  (watching ${ROOT})`);
+  runDsCheck();
+});