files.id migration in one transaction

A failure after the old parent is dropped would leave files half-converted;
in one transaction it rolls back completely. Tested on a fresh Postgres 17.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

database/migrations/1768620765160_files_bigint.ts

@@ -18,7 +18,7 @@ const TRIGGERS = [
  * rewrite also goes through the WAL (LOG.md 2026-10-05 (8)).
  */
 export default class extends BaseSchema {
-  static disableTransactions = true
+  // One transaction: a failure anywhere leaves files as it was (it drops and recreates the parent).
 
   async up() {
     const q = (sql: string) => this.db.rawQuery(sql)