def proficiency_to_level(proficiency: int) -> str:
    """Map proficiency integer (0-100) to skill level string.

    Boundaries (inclusive on the upper edge):
      0-40  → BEGINNER
      41-60 → INTERMEDIATE
      61-100 → ADVANCED

    Note: these boundaries are the *display* mapping for the UI. The gap
    analysis engine uses separate `LEVEL_THRESHOLDS` (BEGINNER=40,
    INTERMEDIATE=60, ADVANCED=100) against raw proficiency — see
    `apps.analysis.services`.
    """
    if proficiency <= 40:
        return 'BEGINNER'
    elif proficiency <= 60:
        return 'INTERMEDIATE'
    else:
        return 'ADVANCED'