Combine stylix and catppuccin/nix via per-target colors toggle

To use catppuccin/nix ports alongside stylix without both writing colors to the same app, set stylix base16Scheme to catppuccin-<flavor>.yaml and disable only the color half of overlapping stylix targets: stylix.targets.<app>.colors.enable = false (available on mkTarget-based targets like ghostty, btop, fzf, lazygit, starship, zellij, cava, mangohud, opencode). This keeps stylix fonts/opacity on those apps while catppuccin/nix supplies the theme. Non-mkTarget targets such as fish only have .enable. catppuccin/nix has no Claude Code port; generate ~/.claude/themes/<name>.json from lib.importJSON "${config.catppuccin.sources.palette}/palette.json" and set settings.theme = "custom:<name>".