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/sql/users.sql

@@ -32,3 +32,23 @@ CREATE TABLE IF NOT EXISTS `users` (
   KEY `idx_users_deleted_at` (`deleted_at`),
   CONSTRAINT `fk_users_mini_program` FOREIGN KEY (`mini_program_id`) REFERENCES `mini_programs`(`id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+-- 会员订阅（通用能力：可给多个功能做“会员优先/免广告”策略）
+-- 说明：
+-- - 会员判断：存在 `status='active' AND ends_at > NOW()` 的记录即可视为会员
+-- - 如果你不想引入该表，也可以选择在 users 表新增 `vip_expires_at` 字段（但扩展性较弱）
+CREATE TABLE IF NOT EXISTS `user_memberships` (
+  `id` bigint unsigned NOT NULL AUTO_INCREMENT,
+  `created_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  `updated_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  `deleted_at` datetime DEFAULT NULL,
+  `mini_program_id` bigint unsigned NOT NULL,
+  `user_id` bigint unsigned NOT NULL,
+  `plan` varchar(30) NOT NULL COMMENT '例如：month/year/lifetime',
+  `status` varchar(20) NOT NULL COMMENT 'active/canceled/expired',
+  `starts_at` datetime NOT NULL,
+  `ends_at` datetime NOT NULL,
+  PRIMARY KEY (`id`),
+  KEY `idx_membership_user` (`mini_program_id`,`user_id`,`ends_at`),
+  KEY `idx_membership_status` (`mini_program_id`,`user_id`,`status`,`ends_at`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;