feat: configuring shell & add fish shell

devshells/default.nix

@@ -1,8 +1,50 @@
 { pkgs, ... }:
 
-pkgs.mkShell {
+let
+  # MCP wrapper script that ensures Python is available for GUI apps
+  mcpNixosWrapper = pkgs.writeShellScriptBin "mcp-nixos-wrapper" ''
+    export PATH="${pkgs.python3}/bin:${pkgs.uv}/bin:$PATH"
+    exec ${pkgs.uv}/bin/uvx mcp-nixos "$@"
+  '';
+
+  # Generate MCP configs for GUI applications
+  mcpConfigForGUI = pkgs.writeText "mcp_settings.json" (builtins.toJSON {
+    mcpServers = {
+      nixos = {
+        type = "stdio";
+        command = "${mcpNixosWrapper}/bin/mcp-nixos-wrapper";
+        args = [ ];
+      };
+    };
+  });
+
+  # Script to install MCP configs for Claude Code and Codex
+  installMcpConfigs = pkgs.writeShellScriptBin "install-mcp-configs" ''
+    set -e
+    echo "Installing MCP configurations..."
+
+    mkdir -p "$HOME/.config/claude-code"
+    mkdir -p "$HOME/.config/codex"
+
+    cp ${mcpConfigForGUI} "$HOME/.config/claude-code/mcp_settings.json"
+    cp ${mcpConfigForGUI} "$HOME/.config/codex/mcp_settings.json"
+
+    echo "✓ Installed MCP config to ~/.config/claude-code/mcp_settings.json"
+    echo "✓ Installed MCP config to ~/.config/codex/mcp_settings.json"
+    echo ""
+    echo "Restart Claude Code and Codex to apply changes."
+  '';
+
+in pkgs.mkShell {
   name = "default";
-  packages = with pkgs; [ git nixfmt-classic uv ];
+  packages = with pkgs; [
+    git
+    nixfmt-classic
+    uv
+    python3
+    mcpNixosWrapper
+    installMcpConfigs
+  ];
   shellHook = ''
     export DOTFILES_ROOT="$PWD"
     export XDG_CACHE_HOME="$DOTFILES_ROOT/.cache"
@@ -18,5 +60,8 @@ pkgs.mkShell {
 
     echo "Loaded default shell for dotfiles development"
     echo "MCP helper alias ready: mcp-nixos"
+    echo ""
+    echo "To install MCP configs for Claude Code and Codex, run:"
+    echo "  install-mcp-configs"
   '';
 }