Add rename-user SQL template; make batch transaction handling robust against non-Postgres backends

- New 'rename-user' template (templates / template rename-user <old> <new>):
  best-effort uid rename across core tables (oc_users, oc_preferences,
  oc_group_user, oc_group_admin, oc_ldap_user_mapping, oc_share, oc_mounts,
  oc_storages). Explicitly NOT a supported Nextcloud operation - the
  generated script carries an in-line warning (as leading SQL comments)
  that app-specific tables (Talk, Calendar, Contacts, Mail, 2FA/WebAuthn...)
  are not covered and that the data directory must be renamed on disk
  manually, followed by occ files:scan --all. Documented the same caveat
  in both READMEs.
- Hardened the round-2 transaction wrapping: beginTransaction()/commit()/
  rollBack() are now wrapped in try/catch. PostgreSQL (our backend) has
  fully transactional DDL so this wasn't actually broken here, but
  Nextcloud also supports MySQL/MariaDB via the same IDBConnection, where
  DDL implicitly commits - on that backend a DDL statement in the batch
  would make a later commit()/rollBack() throw 'no active transaction'
  and previously that exception was unhandled (HTTP 500 instead of a
  clean JSON response). Now: if rollBack() itself fails after an error,
  we report rollbackFailed+warning instead of falsely claiming rolledBack,
  since earlier statements in that batch may already be permanently
  applied. If commit() fails with nothing to commit (already
  auto-committed), that's logged only, since the effects are already
  durably persisted.

js/index.js

@@ -103,6 +103,42 @@
             "SELECT * FROM oc_ldap_user_mapping WHERE owncloud_name = '" + v + "'"
           ].join(';\n') + ';';
         }
+      },
+      'rename-user': {
+        args: ['old_uid', 'new_uid'],
+        description: 'ВНИМАНИЕ: не официальная операция Nextcloud. Переименовывает uid только в основных таблицах ядра — покрывает не всё, требует ручных доп. шагов (см. предупреждение в самом скрипте)',
+        build: function (oldUid, newUid) {
+          var o = escapeSqlString(oldUid);
+          var n = escapeSqlString(newUid);
+          // Предупреждение — только однострочные "--"-комментарии без ";" внутри,
+          // поэтому splitStatements() (парный на бэкенде и здесь) не разобьёт их
+          // как отдельные запросы, а stripLeadingComments() на бэкенде уберёт
+          // этот блок перед определением типа самого первого запроса (SELECT).
+          var warning =
+            "-- WARNING rename is NOT an officially supported Nextcloud operation\n" +
+            "-- This only updates core tables below - it does NOT cover app-specific\n" +
+            "-- tables (Talk, Calendar, Contacts, Mail, two-factor, WebAuthn, etc.)\n" +
+            "-- After running this you must ALSO, with the web server stopped or in\n" +
+            "-- maintenance mode, rename the data directory on disk (data/" + o + " -> data/" + n + ")\n" +
+            "-- and then run: occ files:scan --all\n" +
+            "-- Back up the database first and test on a non-critical account\n";
+          var statements = [
+            "SELECT uid FROM oc_users WHERE uid = '" + o + "'",
+            "SELECT uid FROM oc_users WHERE uid = '" + n + "'",
+            "UPDATE oc_users SET uid = '" + n + "' WHERE uid = '" + o + "'",
+            "UPDATE oc_preferences SET userid = '" + n + "' WHERE userid = '" + o + "'",
+            "UPDATE oc_group_user SET uid = '" + n + "' WHERE uid = '" + o + "'",
+            "UPDATE oc_group_admin SET uid = '" + n + "' WHERE uid = '" + o + "'",
+            "UPDATE oc_ldap_user_mapping SET owncloud_name = '" + n + "' WHERE owncloud_name = '" + o + "'",
+            "UPDATE oc_share SET uid_owner = '" + n + "' WHERE uid_owner = '" + o + "'",
+            "UPDATE oc_share SET uid_initiator = '" + n + "' WHERE uid_initiator = '" + o + "'",
+            "UPDATE oc_share SET share_with = '" + n + "' WHERE share_with = '" + o + "' AND share_type = 0",
+            "UPDATE oc_mounts SET user_id = '" + n + "' WHERE user_id = '" + o + "'",
+            "UPDATE oc_storages SET id = 'home::" + n + "' WHERE id = 'home::" + o + "'",
+            "SELECT uid FROM oc_users WHERE uid = '" + n + "'"
+          ];
+          return warning + statements.join(';\n') + ';';
+        }
       }
     };
 
@@ -218,6 +254,8 @@
       });
       if (response.rolledBack) {
         term.echo('[[;#ff5555;]Batch failed partway through — all statements in this batch were rolled back.]');
+      } else if (response.rollbackFailed) {
+        term.echo('[[;#ff0000;]' + $.terminal.escape_formatting(response.warning || 'Batch failed and the rollback itself failed — earlier statements may have been permanently applied. Check manually.') + ']');
       }
     }