Pagination and filtering for list endpoints

[sugan0tech]

• Description: Add pagination, sorting, and basic filtering to list endpoints.
• Current state: Endpoints like /api/space/all, /api/elements, /api/maps, and /api/usersessions return full lists.
• Tasks:
  • Introduce Spring Data Pageable in repositories/services and expose page, size, sort query params.
  • Add filters where appropriate (e.g., by creatorId, name contains, isValid).
• Acceptance criteria:
  • List endpoints accept pagination/filter params and return paged responses with metadata.
• References: SpaceController.java, ElementService.java, MapService.java, UserSessionController.java.