I just updated the git repo and project description to reflect the new version that I've been testing. The circuit has a much lower part count now, just four passives and the two ICs. The tradeoff is that the microcontroller GPIO pin must never be driven HIGH. When it's driven LOW, it shorts half the resistor divider for the TLVH431, which causes the TLVH431 to send its V_out as high as possible. When the GPIO pin is set to its High-Impedance state, the resistor divider sets V_out to 2.0V and pulls current away from the LED (without shutting off the microcontroller in the process). Driving the GPIO high would push V_outdown to 1.24 V which would definitely shut off the microcontroller.

Pictures are in the updated project description! PCBs should arrive in a week!