fix(sql): purge stranded legacy remote-storage columns (MySQL 8 safe)

02.52.25.sql used `DROP COLUMN IF EXISTS` (MariaDB-only), which errors on
Oracle MySQL 8.x — so on MySQL 8 installs the 26 legacy remote_storage/ftp_*/
sftp_*/gdrive_*/s3_* columns were never dropped, yet Joomla recorded the schema
as applied (confirmed on suite.dev: MySQL 8.0.41, all 26 columns still present,
0 profiles with legacy remote data).

New 02.56.01 migration removes them portably: an INFORMATION_SCHEMA-gated
prepared-statement ALTER that drops all 26 columns where present (plain
DROP COLUMN, valid on MySQL 8 + MariaDB) and is a no-op where already gone
(so it's safe on already-migrated installs too). Validated non-destructively
against suite.dev (gate=1, ALTER PREPAREs cleanly).

Claude-Session: https://claude.ai/code/session_01WbGBN9VyRK61zczYWcCQ2i

source/packages/com_mokosuitebackup/sql/updates/mysql/02.56.01.sql

@@ -0,0 +1,32 @@
+-- Purge legacy single-remote storage columns from installs where they are still present.
+--
+-- Background: 02.52.25.sql originally used `DROP COLUMN IF EXISTS`, which is a
+-- MariaDB-only extension and errors on Oracle MySQL 8.x. On MySQL 8 installs the
+-- migration failed but Joomla still recorded the schema as applied, leaving all 26
+-- legacy remote_storage/ftp_*/sftp_*/gdrive_*/s3_* columns stranded on the profiles
+-- table. This migration removes them portably.
+--
+-- It must be safe on BOTH engines AND on installs where the columns are already gone
+-- (MariaDB, or anyone who ran the corrected 02.52.25). Plain `DROP COLUMN` errors when
+-- a column is absent, and `DROP COLUMN IF EXISTS` errors on MySQL 8 — so neither works
+-- unconditionally. We gate the drop on INFORMATION_SCHEMA and build the ALTER via a
+-- prepared statement, which runs on MySQL 8 and MariaDB alike. All 26 columns were
+-- created and dropped together, so the presence of `remote_storage` gates the whole set.
+-- When the columns are absent this is a no-op (`DO 0`).
+
+SET @moko_has_legacy_remote := (
+    SELECT COUNT(*)
+    FROM INFORMATION_SCHEMA.COLUMNS
+    WHERE TABLE_SCHEMA = DATABASE()
+      AND TABLE_NAME = '#__mokosuitebackup_profiles'
+      AND COLUMN_NAME = 'remote_storage'
+);
+
+SET @moko_drop_legacy_remote := IF(@moko_has_legacy_remote > 0,
+    'ALTER TABLE `#__mokosuitebackup_profiles` DROP COLUMN `remote_storage`, DROP COLUMN `ftp_host`, DROP COLUMN `ftp_port`, DROP COLUMN `ftp_username`, DROP COLUMN `ftp_password`, DROP COLUMN `ftp_path`, DROP COLUMN `ftp_passive`, DROP COLUMN `ftp_ssl`, DROP COLUMN `sftp_host`, DROP COLUMN `sftp_port`, DROP COLUMN `sftp_username`, DROP COLUMN `sftp_auth_type`, DROP COLUMN `sftp_password`, DROP COLUMN `sftp_key_data`, DROP COLUMN `sftp_passphrase`, DROP COLUMN `sftp_path`, DROP COLUMN `gdrive_client_id`, DROP COLUMN `gdrive_client_secret`, DROP COLUMN `gdrive_refresh_token`, DROP COLUMN `gdrive_folder_id`, DROP COLUMN `s3_endpoint`, DROP COLUMN `s3_region`, DROP COLUMN `s3_access_key`, DROP COLUMN `s3_secret_key`, DROP COLUMN `s3_bucket`, DROP COLUMN `s3_path`',
+    'DO 0'
+);
+
+PREPARE moko_stmt FROM @moko_drop_legacy_remote;
+EXECUTE moko_stmt;
+DEALLOCATE PREPARE moko_stmt;