feat(vim): add vim-tmux-navigator

Vim half of the tmux plugin so Ctrl-h/j/k/l moves seamlessly between vim
splits and tmux panes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyrathorpe/home/editor.nix

@@ -10,6 +10,7 @@
       vim-fugitive
       vim-indent-guides
       catppuccin-vim
+      vim-tmux-navigator # Ctrl-h/j/k/l moves between vim splits and tmux panes
     ];
     settings = {
       expandtab = false;