📦 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/nanoid/non-secure/index.d.ts

@@ -0,0 +1,33 @@
+/**
+ * Generate URL-friendly unique ID. This method uses the non-secure
+ * predictable random generator with bigger collision probability.
+ *
+ * ```js
+ * import { nanoid } from 'nanoid/non-secure'
+ * model.id = nanoid() //=> "Uakgb_J5m9g-0JDMbcJqL"
+ * ```
+ *
+ * @param size Size of the ID. The default size is 21.
+ * @returns A random string.
+ */
+export function nanoid(size?: number): string
+
+/**
+ * Generate a unique ID based on a custom alphabet.
+ * This method uses the non-secure predictable random generator
+ * with bigger collision probability.
+ *
+ * @param alphabet Alphabet used to generate the ID.
+ * @param defaultSize Size of the ID. The default size is 21.
+ * @returns A random string generator.
+ *
+ * ```js
+ * import { customAlphabet } from 'nanoid/non-secure'
+ * const nanoid = customAlphabet('0123456789абвгдеё', 5)
+ * model.id = //=> "8ё56а"
+ * ```
+ */
+export function customAlphabet(
+  alphabet: string,
+  defaultSize?: number
+): (size?: number) => string