Added power-source markers to the rails and renamed the rails:
- VCC now includes J4:VCC, U1:VCC1, J5:2, MEGA1:+5V_1, MEGA1:+5V_3, and the VCC power marker.
- VIN now includes J3:1, MEGA1:VIN, MEGA1:+5V_2, U1:VCC2, and the VIN power marker.
ERC result: the two previous “power input not driven” errors are cleared. One warning remains on PWR_VCC:P1 because the marker symbol has a physical terminal that ERC still treats as floating; it does not affect the actual VCC/VIN rail drive status.