Implement getting pending application requests

[serggalel]

As an Organizer I want to view a list of application requests for a specific competition and stage so that I can review the applicants' details and efficiently accept or reject them.

Assumptions & Constraints
The number of applications per competition could be large, making pagination mandatory to prevent database and frontend overload.

Preconditions

1. The application flow is already created and students can successfully submit applications and organizers can accept or reject them.
2. The requester is authenticated and holds the ORG role.

Business rules
Data Completeness: The list must provide enough context (applicant's email, first name and surname, status etc) so the frontend can render a table without needing to make a separate API call for every single user.

Acceptance Criteria

1. When an Organizer requests the list of applications, the system returns an HTTP 200 OK.
2. Search filters applicants by email, first name and surname, case-insensitively.
3. The endpoint supports pagination via page and size query parameters. By default, the list is sorted by submittedAt in descending order (newest first).

Epic link
#5