feat(schema): 添加 family_member_logs 表（家庭成员变更日志）

cfc-backend/src/main/resources/schema.sql

@@ -3799,3 +3799,20 @@ CREATE TABLE IF NOT EXISTS water_record (
     drunk_at DATETIME,
     created_at DATETIME
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+
+-- =============================================
+-- 家庭成员变更日志表
+-- =============================================
+
+CREATE TABLE IF NOT EXISTS family_member_logs (
+    id           BIGINT AUTO_INCREMENT PRIMARY KEY,
+    family_id    BIGINT       NOT NULL COMMENT '家庭ID',
+    member_id    BIGINT       NOT NULL COMMENT '成员ID',
+    action       VARCHAR(32)  NOT NULL COMMENT '操作: join/leave/update/kick',
+    old_value    VARCHAR(500) COMMENT '旧值',
+    new_value    VARCHAR(500) COMMENT '新值',
+    operator_id  BIGINT       COMMENT '操作人用户ID',
+    created_at   DATETIME     DEFAULT CURRENT_TIMESTAMP,
+    INDEX idx_family_id (family_id),
+    INDEX idx_member_id (member_id)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='家庭成员变更日志';