M1-T07: align docs to single-DB reality and re-export OpenAPI

Rewrite README (single app.db + one alembic_app chain, legacy data moved
once via scripts.migrate_legacy_data, accurate test list) and remove the
Grafana Provisioning section. Update architecture-overview to the unified
data layer (one Base, app-DB engine with WAL) and retire the
alembic_location / alembic_poo sections. Mark M1 done in the roadmap.
Re-export openapi/, which catches the spec up to the already-existing
/config/smtp/test and /public-ip/check endpoints (purely additive; M1's
DB-session dependency swap produced no schema change).

pytest 95 passed; ruff clean (pre-existing only); OpenAPI export idempotent.

docs/roadmap.md

@@ -34,7 +34,7 @@
 
 | 里程碑 | 主题 | 一句话 |
 | --- | --- | --- |
-| **M1** | 单库化地基 | 把三库合并成单一 `app.db`，清理散落数据层，删掉 Grafana |
+| **M1** ✅ | 单库化地基 | 把三库合并成单一 `app.db`，清理散落数据层，删掉 Grafana |
 | **M2** | 前端 v2 | React SPA 取代 Jinja，承载 config + 可视化 + 记录增删改 |
 | **M3** | 开放与移动端（远期试水） | token 鉴权 + React Native 移动端 |
 
@@ -42,7 +42,7 @@
 
 ---
 
-## M1 — 单库化地基
+## M1 — 单库化地基（✅ 已完成）
 
 ### 目标