Narrow the terminal tools excluded from Stylix to nvim alone. nvim keeps
its dedicated gbprod/nord.nvim colorscheme, which is richer than the
base16 mapping Stylix would apply.
tmux and fish are now Stylix-managed. Drop the hand-written Nord colours
from the tmux status bar so Stylix themes the status and pane styles,
keeping the minimal layout (session name plus window list) reapplied
after Stylix so it still wins.
Add Stylix as a flake input and a desktop theming module that resolves a
single Nord base16 scheme across the graphical surface: GTK, Qt, cursor,
and the system monospace font, plus a static Nord wallpaper drawn as a
Polar Night gradient.
Scope the theming to the graphical layer alone. The Stylix targets for
fish (at both system and home-manager level), tmux, and nixvim stay off
so the terminal tools keep their hand-written themes.
