[ImgBot] Optimize images

*Total -- 795.60kb -> 784.44kb (1.4%)

/docs/images/concept-flow-chart.svg -- 32.74kb -> 23.64kb (27.79%)
/docs/images/users-venn.svg -- 0.88kb -> 0.72kb (18.46%)
/docs/images/showcase.svg -- 761.99kb -> 760.08kb (0.25%)

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