fix: scope login audit records by tenant

docs/sql/IM-后台消息与登录审计SQL.sql

@@ -1,8 +1,9 @@
 -- MySQL 8.0. Admin message governance and authentication audit tables.
--- Execute this script in each tenant business database.
+-- Execute this script in the shared meeting_im database; tenant_id provides tenant isolation.
 
 CREATE TABLE IF NOT EXISTS im_user_login_logs (
     id BIGINT NOT NULL AUTO_INCREMENT,
+    tenant_id BIGINT NOT NULL,
     user_id BIGINT NOT NULL,
     username VARCHAR(64) NOT NULL DEFAULT '',
     account_type VARCHAR(24) NOT NULL DEFAULT '',
@@ -24,6 +25,7 @@ CREATE TABLE IF NOT EXISTS im_user_login_logs (
     metadata JSON NULL,
     created_at DATETIME(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3),
     PRIMARY KEY (id),
+    INDEX idx_im_user_login_tenant_time (tenant_id, login_at DESC, id DESC),
     INDEX idx_im_user_login_user_time (user_id, login_at DESC, id DESC),
     INDEX idx_im_user_login_ip_time (ip, login_at DESC, id DESC),
     INDEX idx_im_user_login_device_time (device_id(64), login_at DESC),