feat: 初始化数据库模式并引入AI记账服务。

database/sql/create_notifications_table.sql

@@ -0,0 +1,22 @@
+-- Notifications table
+CREATE TABLE IF NOT EXISTS `notifications` (
+  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
+  `created_at` datetime(3) DEFAULT NULL,
+  `updated_at` datetime(3) DEFAULT NULL,
+  `deleted_at` datetime(3) DEFAULT NULL,
+  `user_id` bigint(20) unsigned NOT NULL,
+  `title` varchar(200) COLLATE utf8mb4_unicode_ci NOT NULL,
+  `content` text COLLATE utf8mb4_unicode_ci NOT NULL,
+  `type` varchar(30) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT 'system',
+  `is_read` tinyint(1) DEFAULT '0',
+  `link` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
+  `read_at` datetime(3) DEFAULT NULL,
+  `related_id` bigint(20) unsigned DEFAULT NULL,
+  PRIMARY KEY (`id`),
+  KEY `idx_notifications_deleted_at` (`deleted_at`),
+  KEY `idx_notifications_user_id` (`user_id`),
+  KEY `idx_notifications_type` (`type`),
+  KEY `idx_notifications_is_read` (`is_read`),
+  KEY `idx_notifications_related_id` (`related_id`),
+  CONSTRAINT `fk_users_notifications` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;