Enhance AI and Redis integration for smoke logging features

- Added AI configuration options to .env.example and config.go for OpenAI integration.
- Implemented Redis caching for session management in main.go and auth middleware.
- Updated smoke logging service to support real smoking time (`smoke_at`) and AI advice retrieval.
- Enhanced API routes to include endpoints for AI advice and unlock functionality for non-members.
- Improved database schema with new tables for AI advice and unlock records.
- Expanded documentation to cover new AI features and Redis caching implementation.

docs/common/redis.md

@@ -0,0 +1,22 @@
+# Redis（可选）
+
+当前项目引入 Redis 的主要目的：缓存 `session_key -> user`，减少每个受保护接口都查询 MySQL（尤其在并发增大时更明显）。
+
+## 什么时候需要
+
+- 访问量变大，MySQL 压力主要来自“鉴权查用户”这种高频读
+- 需要做更复杂的能力：限流、计数、分布式锁、异步队列等
+
+## 配置
+
+见 `.env.example`：
+
+- `REDIS_ADDR`
+- `REDIS_PASSWORD`
+- `REDIS_DB`
+- `REDIS_KEY_PREFIX`
+- `REDIS_SESSION_TTL_SECONDS`
+
+说明：
+- 如果不配置 `REDIS_ADDR`，程序会自动禁用 Redis，行为与之前一致。
+