Update algorithm and API documentation for smoking recovery and motivation features

- Added unified backend calculations for health recovery, savings, and motivation generation in the algorithm documentation.
- Updated API documentation to include new endpoints for retrieving statistics and motivation messages, enhancing clarity on data retrieval processes.
- Revised product documentation to reflect changes in API usage for health recovery and savings calculations, ensuring consistency across all related files.

docs/smoke/ALGORITHM.md

@@ -202,7 +202,9 @@ function calculateDailyTarget(baseline, stage, dayInStage) {
 
 ---
 
-## 5. 健康恢复计算
+## 5. 健康恢复计算（后端统一）
+
+接口：`GET /api/v1/smoke/stats?range=week|month|year`（详见 `docs/smoke/API.md`）
 
 基于医学研究的恢复时间线：
 
@@ -236,7 +238,9 @@ function calculateLungRecovery(smokeFreeMinutes) {
 
 ---
 
-## 6. 省钱计算
+## 6. 省钱计算（后端统一）
+
+接口：`GET /api/v1/smoke/stats?range=week|month|year`（详见 `docs/smoke/API.md`）
 
 ```javascript
 // utils/money.js
@@ -250,7 +254,9 @@ function calculateMoneySaved(packPriceCent, cigsPerPack, baselineCigsPerDay, act
 
 ---
 
-## 7. 激励语生成
+## 7. 激励语生成（后端统一）
+
+接口：`GET /api/v1/smoke/motivation`（详见 `docs/smoke/API.md`）
 
 根据用户状态生成不同的激励语：