fix(schemas/theme.json): add light{white,black,gray} colors

[AminurAlam]

light black and light white are standard colors in terminal so i added those

i dont know where the lightgray colors is from but it works without errors so i added that too

here background for 2 is using lightblack

[uncenter]

These colors are not listed as options under https://yazi-rs.github.io/docs/plugins/aliases/#as-color, which this list is based on. Maybe pull request to Yazi itself or the documentation first.

[AminurAlam]

after some more testing seems like these colors are just alias to already existing colors

closing this pr