📦 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/@webassemblyjs/ieee754/src/index.js

@@ -0,0 +1,47 @@
+// @flow
+
+import { write, read } from "@xtuc/ieee754";
+
+/**
+ * According to https://webassembly.github.io/spec/binary/values.html#binary-float
+ * n = 32/8
+ */
+export const NUMBER_OF_BYTE_F32 = 4;
+
+/**
+ * According to https://webassembly.github.io/spec/binary/values.html#binary-float
+ * n = 64/8
+ */
+export const NUMBER_OF_BYTE_F64 = 8;
+
+export const SINGLE_PRECISION_MANTISSA = 23;
+
+export const DOUBLE_PRECISION_MANTISSA = 52;
+
+export function encodeF32(v: number): Array<number> {
+  const buffer = [];
+
+  write(buffer, v, 0, true, SINGLE_PRECISION_MANTISSA, NUMBER_OF_BYTE_F32);
+
+  return buffer;
+}
+
+export function encodeF64(v: number): Array<number> {
+  const buffer = [];
+
+  write(buffer, v, 0, true, DOUBLE_PRECISION_MANTISSA, NUMBER_OF_BYTE_F64);
+
+  return buffer;
+}
+
+export function decodeF32(bytes: Array<Byte>): number {
+  const buffer = new Uint8Array(bytes);
+
+  return read(buffer, 0, true, SINGLE_PRECISION_MANTISSA, NUMBER_OF_BYTE_F32);
+}
+
+export function decodeF64(bytes: Array<Byte>): number {
+  const buffer = new Uint8Array(bytes);
+
+  return read(buffer, 0, true, DOUBLE_PRECISION_MANTISSA, NUMBER_OF_BYTE_F64);
+}