test(hooks): enhance focus-trap mutation score to 85.25% and finalize release acceptance

- Increase use-focus-trap mutation score from 42.62% to 85.25% (exceeds 50% target)
- Add 40 new test cases: focus cycling, Edge Cases, Focusable Elements Detection
- Fix jsdom offsetParent limitation via prototype-level mock
- Remove temporary debug file (__debug.test.tsx)
- Update test-strategy-plan.md to v1.9 with mutation score and debt tracking
- Update README.md with final acceptance progress
- Quality gates: TypeScript 0 errors, ESLint 0 errors, 121 suites/1549 tests passed
- Coverage: 73.62% stmts / 82.52% branches (all thresholds met)

README.md

@@ -32,6 +32,12 @@
   - seo/ 组件覆盖率提升至 100%（新增 24 个测试，覆盖全部 7 个组件）
   - analytics/ 7 组件全覆盖，新增至覆盖率监控
   - 测试债务追踪板同步更新，seo 覆盖缺口已解决
+- 2026-08: **封版验收完成** — test-strategy-plan.md 版本 1.9，所有待办任务完成
+  - 121 测试套件 / 1549 条测试全部通过，TypeScript 0 errors，ESLint 0 errors
+  - 覆盖率：global 73.62% stmts / 82.52% branches（全阈值达标）
+  - 变异测试 use-focus-trap.ts 42.62% → 85.25%（超 50% 目标）
+  - 调试文件清理（__debug.test.tsx 删除）
+  - 测试债务追踪板同步更新，变异测试缺口已解决
 
 ## 项目进度