fix(nvim): make the colorscheme optional

Every nvim start on shron printed

  E185: Cannot find color scheme 'gruvbox'

because gruvbox is a vim-plug plugin and :PlugInstall has never run there - the
plugged directory does not exist at all. The config is checked out on all three
machines, so it cannot assume the plugins are present.

silent! is the idiomatic answer: the theme loads where it exists and is skipped
where it does not. The airline settings below need no such treatment; they are
plain variable assignments and are simply ignored when the plugin is absent.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.config/nvim/init.vim

@@ -145,7 +145,12 @@ let mapleader="\<SPACE>"
 " UI Options {
     " Colorscheme options.
     set bg=dark
-    colorscheme gruvbox
+    " silent!, because the colorscheme comes from a vim-plug plugin and this
+    " file is checked out on machines where :PlugInstall has never run. Without
+    " it every nvim start on shron printed
+    "   E185: Cannot find color scheme 'gruvbox'
+    " A missing theme is not worth an error; the default one works.
+    silent! colorscheme gruvbox
 
     " Also highlight all tabs and trailing whitespace characters.
     highlight ExtraWhitespace ctermbg=darkgreen guibg=darkgreen