My led is blinking at 1 Hz, It normally blink once but sometimes I can see it blinking twice. (approx. quarter of the time)
I've started pibus without -b option to test but the phone button doesn't either switch the video.
I've tested voltage PB0 and Pin 10 of attiny (given as GND in your schemas), and it's always 0.
I'm sure of Q4 is similar to Q2 and Q3 which seems to be good regarding your parts list.
Do you think removing Q4 will change something on PB0 voltage ?