5V Vin Regulates to 5V at Mega
5V needs to go to 5V. Vin feeds the 5V regulator, you will not get 5V out if you put 5V in.
RESET 10uF to GND
What's that do? To my mind, that just keeps the Uno in Reset state, as such it cannot be used to Bootload the 1281.
You need a Programmer to install the 1281 bootload code.
Nick Gammon's code can run on an Uno to program a 1281.
My standalone programmer runs that code, and can be tweaked to set the fuses to kick off the bootloader after a reset.
