📦 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/@bcoe/v8-coverage/src/lib/compare.ts

@@ -0,0 +1,40 @@
+import { FunctionCov, RangeCov, ScriptCov } from "./types";
+
+/**
+ * Compares two script coverages.
+ *
+ * The result corresponds to the comparison of their `url` value (alphabetical sort).
+ */
+export function compareScriptCovs(a: Readonly<ScriptCov>, b: Readonly<ScriptCov>): number {
+  if (a.url === b.url) {
+    return 0;
+  } else if (a.url < b.url) {
+    return -1;
+  } else {
+    return 1;
+  }
+}
+
+/**
+ * Compares two function coverages.
+ *
+ * The result corresponds to the comparison of the root ranges.
+ */
+export function compareFunctionCovs(a: Readonly<FunctionCov>, b: Readonly<FunctionCov>): number {
+  return compareRangeCovs(a.ranges[0], b.ranges[0]);
+}
+
+/**
+ * Compares two range coverages.
+ *
+ * The ranges are first ordered by ascending `startOffset` and then by
+ * descending `endOffset`.
+ * This corresponds to a pre-order tree traversal.
+ */
+export function compareRangeCovs(a: Readonly<RangeCov>, b: Readonly<RangeCov>): number {
+  if (a.startOffset !== b.startOffset) {
+    return a.startOffset - b.startOffset;
+  } else {
+    return b.endOffset - a.endOffset;
+  }
+}