📦 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/module-worker/a.js

@@ -0,0 +1,20 @@
+/**
+ * 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 async function(f) {
+  self.postMessage(f());
+}
+
+export function someValue() {
+  return self.String("a");
+}

frontend/node_modules/@surma/rollup-plugin-off-main-thread/tests/fixtures/module-worker/b.js

@@ -0,0 +1,20 @@
+/**
+ * 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 for side-effects (of which there are none)
+// to make sure that a.js gets its own chunk.
+import {someValue} from "./a.js";
+
+export default function() {
+  return someValue();
+}

frontend/node_modules/@surma/rollup-plugin-off-main-thread/tests/fixtures/module-worker/entry.js

@@ -0,0 +1,17 @@
+/**
+ * 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.
+ */
+
+const w = new Worker("./worker.js", { type: "module" });
+w.addEventListener("message", ev => {
+  window.parent.postMessage(ev.data, "*");
+});

frontend/node_modules/@surma/rollup-plugin-off-main-thread/tests/fixtures/module-worker/rollup.config.js

@@ -0,0 +1,4 @@
+module.exports = (config, outputOptions, omt) => {
+  outputOptions.format = "esm";
+  config.plugins = [omt()];
+};

frontend/node_modules/@surma/rollup-plugin-off-main-thread/tests/fixtures/module-worker/worker.js

@@ -0,0 +1,17 @@
+/**
+ * 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 from "./a.js";
+import("./b.js").then(({default: f}) => {
+  a(f);
+})