It’s glow time in Chinatown. Under a slant of sunlight, Viveca Chow reclines, her hair bundled in a cotton towel, as esthetician Diana Wu works a smooth, curved tool over her pronounced cheekbones. This isn’t some cucumber-water-and-pan-flute facial. There are no plush robes or heated beds here at Diana Beauty Spa , tucked between noodle shops on crowded Mott Street — just the rhythmic pressure of Wu’s capable hands and the scent of herbal oil in the air. But for Chow, 30, a Queens content