Function should_use_dedicated_worker 

pub fn should_use_dedicated_worker(
    width: u32,
    height: u32,
    total_budget_mb: u64,
    parallel_workers: usize,
) -> (bool, u64, usize)

Determine if an image should use the dedicated worker for thumbnail generation. Returns (use_dedicated_worker, effective_max_mb, effective_jobs).

Large images that exceed per-worker memory budget get routed to a dedicated worker with full memory budget. Smaller images use the normal parallel worker pool.