📦 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/tailwindcss/lib/util/prefixSelector.js

@@ -0,0 +1,39 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", {
+    value: true
+});
+Object.defineProperty(exports, /**
+ * @template {string | import('postcss-selector-parser').Root} T
+ *
+ * Prefix all classes in the selector with the given prefix
+ *
+ * It can take either a string or a selector AST and will return the same type
+ *
+ * @param {string} prefix
+ * @param {T} selector
+ * @param {boolean} prependNegative
+ * @returns {T}
+ */ "default", {
+    enumerable: true,
+    get: function() {
+        return _default;
+    }
+});
+const _postcssselectorparser = /*#__PURE__*/ _interop_require_default(require("postcss-selector-parser"));
+function _interop_require_default(obj) {
+    return obj && obj.__esModule ? obj : {
+        default: obj
+    };
+}
+function _default(prefix, selector, prependNegative = false) {
+    if (prefix === "") {
+        return selector;
+    }
+    /** @type {import('postcss-selector-parser').Root} */ let ast = typeof selector === "string" ? (0, _postcssselectorparser.default)().astSync(selector) : selector;
+    ast.walkClasses((classSelector)=>{
+        let baseClass = classSelector.value;
+        let shouldPlaceNegativeBeforePrefix = prependNegative && baseClass.startsWith("-");
+        classSelector.value = shouldPlaceNegativeBeforePrefix ? `-${prefix}${baseClass.slice(1)}` : `${prefix}${baseClass}`;
+    });
+    return typeof selector === "string" ? ast.toString() : ast;
+}