(diff themes) wrong color options

The diff themes (and the whiskers template) don't match the kitty settings.

I don't really know, but I'm assuming that kitty changed its config somewhat recently, and despite the regular themes using `color0`, `color1`, etc. the diff themes don't, and still use options like `search_bg` and `search_fg`, that are not recognized by kitty.

Compare the diff themes and the whiskers template with the current Kitty settings, focusing on the color options used by regular themes versus options such as search_bg and search_fg. Confirm which options Kitty recognizes, update the inconsistent theme definitions, and verify that the resulting themes load without unrecognized-setting warnings.

Written by the indexing model from the issue text.