Fix tmux and nvim color display issues

- Add COLORTERM=truecolor to zsh session variables for 24-bit color support
- Update tmux terminal overrides to match xterm-256color terminal type
- Add gruvbox-nvim plugin and set explicit background=dark in nvim config
- Replace default colorscheme with gruvbox to match lualine theme

🤖 Generated with [Claude Code](https://claude.ai/code)

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

flake.nix

@@ -52,6 +52,9 @@
         enable = true;
         defaultKeymap = "viins";
         enableVteIntegration = true;
+        sessionVariables = {
+          COLORTERM = "truecolor";
+        };
       };
     };
   in

nvim.nix

@@ -9,6 +9,7 @@
       nvim-treesitter.withAllGrammars
       lualine-nvim
       nvim-web-devicons
+      gruvbox-nvim
     ];
     extraLuaConfig = ''
       -- Basic settings
@@ -31,7 +32,8 @@
       vim.g.mapleader = " "
 
       -- Set gruvbox colorscheme to match lualine theme
-      vim.cmd('colorscheme default')  -- Use a simple colorscheme that works with lualine
+      vim.opt.background = "dark"
+      vim.cmd('colorscheme gruvbox')
 
       -- Nvim-tree setup
       require("nvim-tree").setup({})

tmux.nix

@@ -12,7 +12,7 @@
     extraConfig = ''
       # Terminal settings
       set -g default-terminal "screen-256color"
-      set -ga terminal-overrides ",*256col*:Tc"
+      set -ga terminal-overrides ",xterm-256color:Tc"
       
       # Gruvbox Dark Theme
       # Status bar colors