fix(migrations): MariaDB 兼容幂等化 privacy_mode 列与 distributions 种子插入

migrations/mig_g5_privacy.sql

@@ -84,6 +84,11 @@ CREATE TABLE IF NOT EXISTS usage_reports (
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
 
 -- 5. Add privacy_mode to distributions table
-ALTER TABLE distributions 
-    ADD COLUMN IF NOT EXISTS privacy_mode ENUM('local', 'cloud', 'hybrid') NOT NULL DEFAULT 'cloud' 
-    COMMENT 'Deployment mode for distribution' AFTER status;
+-- MariaDB 11.8 不支持 ADD COLUMN IF NOT EXISTS 语法，改用 information_schema 预检 + 动态 PREPARE 实现幂等
+SET @exist_pm := (SELECT COUNT(*) FROM information_schema.COLUMNS WHERE TABLE_SCHEMA = 'aiflow' AND TABLE_NAME = 'distributions' AND COLUMN_NAME = 'privacy_mode');
+SET @sql_pm := IF(@exist_pm = 0,
+    "ALTER TABLE distributions ADD COLUMN privacy_mode ENUM('local', 'cloud', 'hybrid') NOT NULL DEFAULT 'cloud' COMMENT 'Deployment mode for distribution' AFTER status",
+    'SELECT 1');
+PREPARE stmt_pm FROM @sql_pm;
+EXECUTE stmt_pm;
+DEALLOCATE PREPARE stmt_pm;