CVE-2026-63460: Vendure: Unauthenticated ReDoS via `regex` filter on SQLite backends

[!IMPORTANT] Only instances running on the SQLite driver (better-sqlite3) are affected; SQLite is usually used in development/testing backend, so production deployments on PostgreSQL or MySQL/MariaDB are unaffected.

The StringOperators.regex filter exposed on the public Shop GraphQL API is evaluated inside the Node.js event loop via a synchronous SQLite user-defined function (UDF). Supplying a catastrophically backtracking pattern blocks the entire event loop, causing a complete denial of service with no authentication required.