Correct completion menu current item color styling

[ivnvxd]

This PR fixes an issue where the completion-menu-current-color and completion-menu-current-bg-color properties were incorrectly applied.

Previously:

• completion-menu-current-color was setting the background color
• completion-menu-current-bg-color was setting the text color

This was backwards from the expected behavior and from how prompt_toolkit's default styling works (where fg sets text color and bg sets background color).

The fix

• Swapped the color assignments so:
  • completion-menu-current-color now properly sets the text color
  • completion-menu-current-bg-color now properly sets the background color

This matches prompt_toolkit's default styling pattern seen in defaults.py:

 ("completion-menu.completion.current", "fg:#888888 bg:#ffffff reverse")

Now when using:

• completion-menu-current-color: blue
• completion-menu-current-bg-color: red

The selected completion item will show:

• Blue text on a red background (instead of the previous red text on blue background)

This provides more intuitive color configuration and matches the expected styling behavior.