nvim: init: Disable virtual text for all diagnostics

They frequently get clipped beyond the window border due to being too
long and are not that helpful.

While at it, use our own preferable default sane options for the rest.

nvim/.config/nvim/init.lua

@@ -95,6 +95,20 @@ vim.g.dispatch_no_maps            = 1
 -- We do this to prevent the loading of the system fzf.vim plugin. This is
 -- present at least on Arch/Manjaro
 vim.api.nvim_command('set rtp-=/usr/share/vim/vimfiles')
+-- Disable virtual text for all diagnostics
+vim.diagnostic.config({
+  underline        = true,
+  signs            = true,
+  virtual_text     = false,
+  update_in_insert = false,
+  severity_sort    = true,
+  float = {
+    show_header = false,
+    source      = 'always',
+    border      = 'rounded',
+    focusable   = false,
+  },
+})
 
 require 'plugins'
 require 'autocmd'