feat: add benchmark suite with QuickJS=80 baseline scoring

- build.sh: auto-detect package manager, install deps, build OxideJS + QuickJS
- run_benchmark.py: full test262 (--no-skip), stress benchmarks, timing, AI agent score
- fetch_test262.sh: download test262 test suite
- README.md: usage instructions and scoring formula

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
(cherry picked from commit ecaf9ac049b70a9ff518d778886e3fd55287c252)

benchmark/fetch_test262.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+# 下载 test262 测试套件到仓库 tests/ 目录
+set -e
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$REPO_ROOT/tests"
+if [ -d test262/test ]; then
+    echo "test262 已存在: $(find test262/test -name '*.js' | wc -l) 测试"
+    exit 0
+fi
+echo "下载 test262 (约 500MB)..."
+git clone --depth 1 https://github.com/tc39/test262.git test262
+echo "完成"