meta: Replace zellij with tmux

Now that tmux works again, it makes sense to choose it over zellij due
to the vastly superior community support around it. Using tmux-256color
makes colors work properly in programs like htop, and neovim benefits
from squiggly lines and italics from kitty as well.

home/tmux.nix

@@ -0,0 +1,24 @@
+{
+  programs.tmux = {
+    enable = true;
+    mouse = true;
+
+    keyMode = "vi";
+
+    extraConfig = /* fish */ ''
+      set -sg escape-time 0
+
+      set -g renumber-windows on
+      set -g status-right ""
+      set -g status-left ""
+      set -g status-justify centre
+      set -g status-bg black
+      set -g status-fg white
+      set -g default-terminal "tmux-256color"
+
+      bind -n S-Left previous-window
+      bind -n S-Right next-window
+      bind -n S-Up set status
+    '';
+  };
+}

modules/shell.nix

@@ -71,7 +71,6 @@ in
         inherit (pkgs)
           gdu
           hexyl
-          zellij
           diskonaut
           pgcli
           litecli