Relay parallel to wall switch: Is it safe?
You can use the same way as good old days alternating switch.



simulate this circuit &ndash; Schematic created using CircuitLab
You could use a dual coil latching relay. You send a short pulse to a coil to change the position. Probably you need also a measuring circuit the can determine whether the light is turned on or off. If the smart electronics fail, you still have the wall switch.
This is how similar device looks like, you install it directly into a electric wall box.