Down on McLean Avenue the city runs right up against the Bronx line, and on a September evening the block smells like cut grass and somebody's dinner at the same time. Puente Landscaping Inc. keeps the small front lawns along there and up through the streets above — mowing on schedule, trimming close to fences and stoops, edging where concrete meets green. Beds get weeded and mulched; hedges get taken back before they lean over the sidewalk. Autumn means leaves, bagged and gone, and April means the cleanup that wakes a yard up again. In a dense corner of Yonkers, a tidy lawn is a small public gift.