feat: add Full-Text Search (FTS) lookups for PostgreSQL

[Einswilli]

Currently, Ryx supports basic string lookups. Adding native PostgreSQL Full-Text Search would significantly improve querying capabilities for text-heavy apps.

Goal: Implement a new lookup (e.g., search) that generates PostgreSQL to_tsvector and to_tsquery SQL.

Implementation hint:

1. Add the lookup logic in ryx-query's lookup registry.
2. Ensure it handles the correct SQL syntax for Postgres while providing a fallback or a clear error for other backends.