Make shed light come on, if dark outside and door is open (with NPN and hall-effect sensor)
Assuming your magnet is pulling down the hall sensor's output pin, the simplest solution is to put the A3144 in parallel with your photoresistor. Connect pin1 to VCC, pin2 to GND, and pin3 to the upper end of the photoresistor.

This way when there is sunlight, the transistor's base will be pulled down (through the series resistor) to the GND. When the magnet is close to the sensor (door closed), the hall effect sensor pulls this down. Without light or magnet, your potentiometer pulls up the base and the light switches on.

You need to check the appropriate voltages, safe current (A3144 tolerates up to 28V and 25mA), etc. when your other components are known. (probably okay)