Add directional options to `Resize` action:

Add directional options to `Resize` action:

This introduces an optional "direction" argument to the Resize action,
mirroring Fluxbox's StartResizing [corner] behavior.

Supported values (case-insensitive) are:
up-left, up, up-right, left, right, down-left, down, down-right.

If no direction is specified, the existing behavior is preserved and the
resize edges are inferred from the current pointer position. The action
documentation has been updated to describe the new argument.