📦 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/postcss-normalize-timing-functions/src/index.js

@@ -0,0 +1,146 @@
+'use strict';
+const valueParser = require('postcss-value-parser');
+
+/** @type {(node: valueParser.Node) => number} */
+const getValue = (node) => parseFloat(node.value);
+
+/* Works because toString() normalizes the formatting,
+   so comparing the string forms behaves the same as number equality*/
+const conversions = new Map([
+  [[0.25, 0.1, 0.25, 1].toString(), 'ease'],
+  [[0, 0, 1, 1].toString(), 'linear'],
+  [[0.42, 0, 1, 1].toString(), 'ease-in'],
+  [[0, 0, 0.58, 1].toString(), 'ease-out'],
+  [[0.42, 0, 0.58, 1].toString(), 'ease-in-out'],
+]);
+/**
+ * @param {valueParser.Node} node
+ * @return {void | false}
+ */
+function reduce(node) {
+  if (node.type !== 'function') {
+    return false;
+  }
+
+  if (!node.value) {
+    return;
+  }
+
+  const lowerCasedValue = node.value.toLowerCase();
+
+  if (lowerCasedValue === 'steps') {
+    // Don't bother checking the step-end case as it has the same length
+    // as steps(1)
+    if (
+      node.nodes[0].type === 'word' &&
+      getValue(node.nodes[0]) === 1 &&
+      node.nodes[2] &&
+      node.nodes[2].type === 'word' &&
+      (node.nodes[2].value.toLowerCase() === 'start' ||
+        node.nodes[2].value.toLowerCase() === 'jump-start')
+    ) {
+      /** @type string */ (node.type) = 'word';
+      node.value = 'step-start';
+
+      delete (/** @type Partial<valueParser.FunctionNode> */ (node).nodes);
+
+      return;
+    }
+
+    if (
+      node.nodes[0].type === 'word' &&
+      getValue(node.nodes[0]) === 1 &&
+      node.nodes[2] &&
+      node.nodes[2].type === 'word' &&
+      (node.nodes[2].value.toLowerCase() === 'end' ||
+        node.nodes[2].value.toLowerCase() === 'jump-end')
+    ) {
+      /** @type string */ (node.type) = 'word';
+      node.value = 'step-end';
+
+      delete (/** @type Partial<valueParser.FunctionNode> */ (node).nodes);
+
+      return;
+    }
+
+    // The end case is actually the browser default, so it isn't required.
+    if (
+      node.nodes[2] &&
+      node.nodes[2].type === 'word' &&
+      (node.nodes[2].value.toLowerCase() === 'end' ||
+        node.nodes[2].value.toLowerCase() === 'jump-end')
+    ) {
+      node.nodes = [node.nodes[0]];
+
+      return;
+    }
+
+    return false;
+  }
+
+  if (lowerCasedValue === 'cubic-bezier') {
+    const values = node.nodes
+      .filter((list, index) => {
+        return index % 2 === 0;
+      })
+      .map(getValue);
+
+    if (values.length !== 4) {
+      return;
+    }
+
+    const match = conversions.get(values.toString());
+
+    if (match) {
+      /** @type string */ (node.type) = 'word';
+      node.value = match;
+
+      delete (/** @type Partial<valueParser.FunctionNode> */ (node).nodes);
+
+      return;
+    }
+  }
+}
+
+/**
+ * @param {string} value
+ * @return {string}
+ */
+function transform(value) {
+  return valueParser(value).walk(reduce).toString();
+}
+
+/**
+ * @type {import('postcss').PluginCreator<void>}
+ * @return {import('postcss').Plugin}
+ */
+function pluginCreator() {
+  return {
+    postcssPlugin: 'postcss-normalize-timing-functions',
+
+    OnceExit(css) {
+      const cache = new Map();
+
+      css.walkDecls(
+        /^(-\w+-)?(animation|transition)(-timing-function)?$/i,
+        (decl) => {
+          const value = decl.value;
+
+          if (cache.has(value)) {
+            decl.value = cache.get(value);
+
+            return;
+          }
+
+          const result = transform(value);
+
+          decl.value = result;
+          cache.set(value, result);
+        }
+      );
+    },
+  };
+}
+
+pluginCreator.postcss = true;
+module.exports = pluginCreator;