There're a lot of people who solved this, so I may have missed something.. but I feel the definition of the move is little unclear.

I think there are several possibility of the consequence of "up". for example, applying "up" on the following board

[1, 2, 3],
[4, 6, 8],
[7, 0, 5]

can yield

[1, 2, 3],
[4, 0, 6],
[7, 5, 8]  # (shifting the right side)

or

[1, 2, 3],
[6, 0, 8],
[4, 7, 5] # (shifting the left side)

or even

[1, 6, 2],
[4, 0, 3],
[7, 5, 8]  # (shifting 2x3 cells on right side)

could you clarify what will be the result of move for each direction, or is it the part of this task?