Implement search through given userIds

[serggalel]

As a Developer I want to expose a candidate-based text search method in the UserFacade so that other modules can filter specific subsets of users by name or email without violating Modulith database boundaries.

Assumptions & Constraints

1. To prevent scanning the entire database, the search must be restricted to a provided list of candidateIds.
2. Search inputs must be heavily sanitized to prevent SQL Wildcard Injection (e.g., treating % and _ as literal characters, not wildcards).

Preconditions
The User database entity contains firstName, surname, and email.

Acceptance Criteria

1. The UserFacade defines the method: Optional<List> findUserIdsBySearch(String search, List candidateIds).
2. If the search string is null, empty, or only whitespace, the method returns Optional.empty(). (This signals to the caller that no filtering occurred).
3. The service normalizes the search string by trimming it, collapsing multiple spaces into a single space, and escaping SQL wildcards (, %, _).