本地启动环境修复与配置

- config.yaml: checkpointer 连接串改为相对路径(原为他机绝对路径,本地无法创建)
- frontend-web: 补充缺失的 dayjs 直接依赖(lockfile 已有,package.json 缺失)
- .gitignore: 忽略 backend/uv.lock 并取消其跟踪

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -98,3 +98,6 @@ docs/aidev-docs
 docs/backups
 # Frontend skills components must be tracked (excluded from the broad skills/ ignore above)
 !frontend-web/src/components/workspace/skills/
+
+# uv lockfile (not tracked per project preference)
+offline-backend-20260512/backend/uv.lock