refactor(neovim): migrate to extraLuaConfig 🎨

Move Lua config out of VimScript heredoc into proper extraLuaConfig.
Use vim.opt and vim.keymap.set instead of legacy set/nnoremap.
Keep VimScript only for settings that are simpler in vim (colorscheme,
netrw, let g: vars).

nixos/neovim.nix

@@ -4,71 +4,59 @@
   programs.neovim = {
     enable = true;
     defaultEditor = true;
-    # TODO: refactor (some parts) to extraLuaConfig
+
+    # VimScript settings (options that have no Lua equivalent or are simpler in vim)
     extraConfig = ''
       set title
-      set mouse=a
       set nohlsearch
       set number
       let mapleader=","
 
-      lua << EOF
-        local config_file = os.getenv("HOME")..'/.local/share/nvim_color_scheme'
-        local f = io.open(config_file, "r")
-        if f ~= nil then
-            local system_theme = f:read("*l")
-            io.close(f)
-            if system_theme then
-                system_theme = system_theme:gsub("^%s+", ""):gsub("%s+$", "")
-            end
-            if system_theme == 'dark' then
-                vim.cmd("set bg=dark")
-            elseif system_theme == 'light' then
-                vim.cmd("set bg=light")
-            else
-                print('warning: expected value "light" or "dark"')
-                print('  got:', system_theme)
-                print('  expected path:', config_file)
-            end
-        else
-            print('warning: nvim color scheme not found')
-            print('  expected path:', config_file)
-        end
-      EOF
-
-      colorscheme catppuccin " catppuccin-latte, catppuccin-frappe, catppuccin-macchiato, catppuccin-mocha
+      colorscheme catppuccin
 
       " netrw (dir listing) settings
       let g:netrw_liststyle = 3
       let g:netrw_banner = 0
       let g:netrw_browse_split = 3
-      let g:netrw_winsize = 25  " % of page
+      let g:netrw_winsize = 25
+    '';
 
-      set listchars=tab:→\ ,space:·,nbsp:␣,trail:•,eol:¶,precedes:«,extends:»
-      set clipboard+=unnamedplus
+    extraLuaConfig = ''
+      -- Auto-detect system theme (dark/light) from marker file
+      local config_file = os.getenv("HOME") .. "/.local/share/nvim_color_scheme"
+      local f = io.open(config_file, "r")
+      if f then
+        local theme = f:read("*l")
+        f:close()
+        if theme then
+          theme = theme:gsub("^%s+", ""):gsub("%s+$", "")
+        end
+        if theme == "dark" or theme == "light" then
+          vim.opt.background = theme
+        else
+          vim.notify("nvim_color_scheme: expected 'light' or 'dark', got: " .. tostring(theme), vim.log.levels.WARN)
+        end
+      end
 
-      " Replace-all is aliased to S.
-      nnoremap S :%s//g<Left><Left>
+      -- General options
+      vim.opt.mouse = "a"
+      vim.opt.listchars = { tab = "→ ", space = "·", nbsp = "␣", trail = "•", eol = "¶", precedes = "«", extends = "»" }
+      vim.opt.clipboard:append("unnamedplus")
+      vim.opt.spell = true
+      vim.opt.spelllang = "en_us"
 
-      " save file with ,w
-      map <leader>w :w<cr><Space>
-
-      " spellcheck
-      set spell spelllang=en_us
-      setlocal spell! spelllang=en_us
+      -- Keymaps
+      vim.keymap.set("n", "S", ":%s//g<Left><Left>", { desc = "Replace all" })
+      vim.keymap.set("n", "<leader>w", ":w<CR>", { desc = "Save file" })
     '';
 
     plugins = with pkgs.vimPlugins; [
       vim-surround    # shortcuts for setting () {} etc.
       vim-gitgutter   # git diff in sign column
-      # vim-airline   # nice and light status bar # doesn't work nicely with tmux
-      # coc-nvim coc-git coc-highlight coc-python coc-rls coc-vetur coc-vimtex coc-yaml coc-html coc-json # auto completion
       vim-nix         # nix highlight
-      # vimtex        # latex stuff - disabled due to build check issue
       fzf-lua         # fuzzy finder through lua
       nerdtree        # file structure inside nvim
       rainbow         # color parenthesis
-      # gruvbox-nvim  # theme
       catppuccin-nvim # theme
       goyo-vim        # write prose
       limelight-vim   # prose paragraph highlighter