📦 添加虚拟环境和启动脚本

新增:
- backend/venv/ - Python 虚拟环境
- backend/start.sh - 启动脚本（使用虚拟环境）
- backend/requirements.txt - 依赖列表
- .gitignore - 忽略虚拟环境和缓存文件

说明:
- 每个项目使用独立虚拟环境
- 避免依赖冲突
- 启动脚本自动创建和激活虚拟环境

frontend/node_modules/@surma/rollup-plugin-off-main-thread/tests/fixtures/amd-function-name/a.js

@@ -0,0 +1,16 @@
+/**
+ * Copyright 2018 Google Inc. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export default function() {
+  return 4;
+}

frontend/node_modules/@surma/rollup-plugin-off-main-thread/tests/fixtures/amd-function-name/config.json

@@ -0,0 +1,3 @@
+{
+  "amdFunctionName": "foo"
+}

frontend/node_modules/@surma/rollup-plugin-off-main-thread/tests/fixtures/amd-function-name/entry.js

@@ -0,0 +1,22 @@
+/**
+ * Copyright 2018 Google Inc. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import("./a.js").then(m => {
+  if (m.default() != 4) {
+    return;
+  }
+  if (!self.foo) {
+    return;
+  }
+  window.parent.postMessage("a", "*");
+});