feat(harness): integrate walkinglabs 5-subsystem model with templates

- Add .harness/ directory with 6 templates:
  init.sh (unified startup entry)
  PROGRESS.md (session progress tracking)
  feature_list.json (machine-readable feature status)
  clean-state-checklist.md (end-of-session cleanup)
  session-handoff.md (cross-session handoff)
  evaluator-rubric.md (review scoring)
- Update AGENTS.md: 5-subsystem model (Instruction/Tools/Environment/State/Feedback)
- Add Init-Plan-Implement-Verify-Cleanup workflow cycle

.harness/clean-state-checklist.md

@@ -0,0 +1,13 @@
+# 干净状态检查清单
+
+会话结束前逐项检查：
+
+- [ ] 标准启动路径仍然可用（mvn compile 通过）
+- [ ] 标准验证路径仍然可运行
+- [ ] 当前进度已记录到 PROGRESS.md
+- [ ] 功能状态真实反映 passing 和未验证的边界
+- [ ] feature_list.json 已更新
+- [ ] 没有任何半成品步骤处于未记录状态
+- [ ] 临时文件和调试代码已清理
+- [ ] 提交信息清晰描述了变更内容
+- [ ] 下一轮会话无需人工修复即可继续