Thanks to some inspiration from this thread, I contributed to the development of Home Assistant Device Bridge! Others had already done the hard work of developing and testing the code necessary to add thermostat devices (@gabriel_kpk @aaiyar), but I was able to submit the pull request (first-time github user here!), add a device state to the driver code, AND submit a pull request for the configuration app so that the thermostats are displayed in the app's discovery drop-down. I'm standing on the shoulders of giants, to be sure, but I've already checked off "learning me some groovy," and it's still 2021! Thanks to @SmartHomePrimer @tomw and @ymerj for helping me along! The HE platform is amazing because the COMMUNITY IS AMAZING! w00t!
P.S. And because of this work, I can rework my HA setup and skip the MQTT broker altogether!