📦 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/css-tree/lib/syntax/pseudo/common/nth.js

@@ -0,0 +1,9 @@
+var DISALLOW_OF_CLAUSE = false;
+
+module.exports = {
+    parse: function nth() {
+        return this.createSingleNodeList(
+            this.Nth(DISALLOW_OF_CLAUSE)
+        );
+    }
+};

frontend/node_modules/css-tree/lib/syntax/pseudo/common/nthWithOfClause.js

@@ -0,0 +1,9 @@
+var ALLOW_OF_CLAUSE = true;
+
+module.exports = {
+    parse: function nthWithOfClause() {
+        return this.createSingleNodeList(
+            this.Nth(ALLOW_OF_CLAUSE)
+        );
+    }
+};

frontend/node_modules/css-tree/lib/syntax/pseudo/common/selectorList.js

@@ -0,0 +1,7 @@
+module.exports = {
+    parse: function selectorList() {
+        return this.createSingleNodeList(
+            this.SelectorList()
+        );
+    }
+};

frontend/node_modules/css-tree/lib/syntax/pseudo/dir.js

@@ -0,0 +1,7 @@
+module.exports = {
+    parse: function() {
+        return this.createSingleNodeList(
+            this.Identifier()
+        );
+    }
+};

frontend/node_modules/css-tree/lib/syntax/pseudo/has.js

@@ -0,0 +1,7 @@
+module.exports = {
+    parse: function() {
+        return this.createSingleNodeList(
+            this.SelectorList()
+        );
+    }
+};

frontend/node_modules/css-tree/lib/syntax/pseudo/index.js

@@ -0,0 +1,12 @@
+module.exports = {
+    'dir': require('./dir'),
+    'has': require('./has'),
+    'lang': require('./lang'),
+    'matches': require('./matches'),
+    'not': require('./not'),
+    'nth-child': require('./nth-child'),
+    'nth-last-child': require('./nth-last-child'),
+    'nth-last-of-type': require('./nth-last-of-type'),
+    'nth-of-type': require('./nth-of-type'),
+    'slotted': require('./slotted')
+};

frontend/node_modules/css-tree/lib/syntax/pseudo/lang.js

@@ -0,0 +1,7 @@
+module.exports = {
+    parse: function() {
+        return this.createSingleNodeList(
+            this.Identifier()
+        );
+    }
+};

frontend/node_modules/css-tree/lib/syntax/pseudo/matches.js

@@ -0,0 +1 @@
+module.exports = require('./common/selectorList');

frontend/node_modules/css-tree/lib/syntax/pseudo/not.js

@@ -0,0 +1 @@
+module.exports = require('./common/selectorList');

frontend/node_modules/css-tree/lib/syntax/pseudo/nth-child.js

@@ -0,0 +1 @@
+module.exports = require('./common/nthWithOfClause');

frontend/node_modules/css-tree/lib/syntax/pseudo/nth-last-child.js

@@ -0,0 +1 @@
+module.exports = require('./common/nthWithOfClause');

frontend/node_modules/css-tree/lib/syntax/pseudo/nth-last-of-type.js

@@ -0,0 +1 @@
+module.exports = require('./common/nth');

frontend/node_modules/css-tree/lib/syntax/pseudo/nth-of-type.js

@@ -0,0 +1 @@
+module.exports = require('./common/nth');

frontend/node_modules/css-tree/lib/syntax/pseudo/slotted.js

@@ -0,0 +1,7 @@
+module.exports = {
+    parse: function compoundSelector() {
+        return this.createSingleNodeList(
+            this.Selector()
+        );
+    }
+};