M6-T11: document M6 (energy pricing + DSMR + Tibber) across README/roadmap/arch

- README: M6 section + feature list + new tables/config items.
- roadmap: M6 row (graduated) + detail section; M6 in milestone index.
- architecture-overview: M6 models/services/integrations/routes/jobs/config.
- design/README: index m6, drop stale '三个里程碑' wording.
- OpenAPI already in sync (no diff).

docs/design/m6-tibber-dynamic-energy.md

@@ -427,7 +427,7 @@ Phase D（API + 前端）
 - **Reviewer checklist**: 全走类型化 client；图表组件隔离复用；表单按结构渲染、不 hardcode 字段；窗口/上限；空/错/加载/缺 key 容错。
 
 ### M6-T11 — 文档 + OpenAPI + roadmap 收尾
-- **Status**: `todo` · **Depends**: 全部
+- **Status**: `done` · **Depends**: 全部
 - **Files**: `modify README.md`、`docs/roadmap.md`（M6 行 + 毕业）、`docs/architecture-overview.md`、`docs/design/README.md`（列入 m6）；`run python scripts/export_openapi.py` 并提交 `openapi/`
 - **Acceptance criteria**:
   - [ ] 文档反映新链路；`git diff --exit-code openapi/` 无未提交差异；校验闸门全绿。