sync: add mandatory pre-execution checklist for screenshots in journey mode

Adds a pre-execution checklist to prevent mistake where:
- browser_snapshot (DOM snapshot) was used instead of browser_take_screenshot (PNG)
- every user step must have browser_take_screenshot for visual verification
- violates any item = interrupt and fix before continuing

This prevents the error where only final screenshot was saved instead of every step.

.claude/skills/d8d-dev/journey-mode.md

@@ -340,6 +340,13 @@ Story 验证全部通过 ≠ 用户能正常使用系统。旅程模式弥补这
 
 ### 执行模板（每条旅程 — 规定式，不得偏离）
 
+⛔ **执行前必须对照检查清单**（违反 = 错误，必须纠正后继续）：
+- [ ] `browser_snapshot` = DOM 结构快照（找元素用），**不是**视觉验证
+- [ ] `browser_take_screenshot` = PNG 截图保存（用于视觉验证），**每个步骤必须**
+- [ ] 每个用户步骤完成 → `browser_take_screenshot` + `analyze_image` → 视觉验证关卡
+- [ ] 旅程最终完成 → `browser_take_screenshot` 最终截图 + `browser_network_requests` 资源检查
+- [ ] 违反任意一条 → 中断补全，不能继续
+
 ```
 对每条旅程: