feat: Execute zone - Playwright PC Web + Appium mobile + AI screenshot diff + test conclusion reports

- Add 3 new agents: web-executor, mobile-executor, result-reporter
- web-executor: Playwright multi-browser (Chromium/Firefox/WebKit) automated scripts
- mobile-executor: Appium dual-platform (Android/iOS) automated scripts
- result-reporter: pixel-level AI visual comparison + test conclusion report with screenshots
- Auto-generate executable Python test scripts from Markdown test cases
- Screenshot strategies: on-failure (default) + on-step (optional)
- Visual diff grading: <1% pass / 1-5% minor / 5-15% UI_DIFF / >15% blocker
- Failure multi-classification: REAL_BUG/UI_DIFF/ENV_ISSUE/DATA_ISSUE/CASE_BUG/SCRIPT_ERROR
- requirements.txt: add playwright + Pillow
- Fleet now: 17 agents across 6 battle zones

AGENTS.md

@@ -25,7 +25,7 @@
 python3 scripts/fleet_runner.py run --requirement <需求文档路径>
 ```
 
-3. fleet_runner.py 自动按战区顺序编排 14 个专业 Agent：
+3. fleet_runner.py 自动按战区顺序编排 17 个专业 Agent：
 
    **PREPARE 战区 (2 Agent):**
    - document-parser: 文档解析标准化
@@ -42,6 +42,11 @@ python3 scripts/fleet_runner.py run --requirement <需求文档路径>
    - case-designer: 用例设计
    - data-builder: 测试数据构造
 
+   **EXECUTE 战区 (3 Agent):**
+   - web-executor: PC Web Playwright 自动化执行 + 截图
+   - mobile-executor: 移动端 Appium 自动化执行 + 截图
+   - result-reporter: AI 视觉对比 + 测试结论报告
+
    **REVIEW 战区 (3 Agent):**
    - case-reviewer: 用例评审
    - coverage-auditor: 覆盖率审计