Initial Nix configuration setup

- Add nix-darwin and home-manager flake configuration
- Include modular neovim setup with plugins and keybinds
- Add tmux configuration with gruvbox theme and vim-like bindings
- Set up .gitignore for nix build outputs and temporary files

Ready for multi-machine deployment across macOS systems.

flake.nix

@@ -0,0 +1,69 @@
+{
+  description = "Default environment";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    nix-darwin.url = "github:nix-darwin/nix-darwin/master";
+    nix-darwin.inputs.nixpkgs.follows = "nixpkgs";
+    home-manager.url = "github:nix-community/home-manager";
+    home-manager.inputs.nixpkgs.follows = "nixpkgs";
+    claude-code.url = "github:sadjow/claude-code-nix";
+  };
+
+  outputs = inputs@{ self, nix-darwin, nixpkgs, home-manager, claude-code }:
+  let
+    configuration = { pkgs, ... }: {
+      environment.systemPackages =
+        [ pkgs.vim
+          pkgs.git
+        ];
+
+      nix.settings.experimental-features = "nix-command flakes";
+      system.stateVersion = 6;
+      nixpkgs.hostPlatform = "aarch64-darwin";
+
+      programs.zsh.enable = true;
+    };
+
+    homeConfiguration = { pkgs, ... }: {
+      imports = [ ./nvim.nix ./tmux.nix ];
+
+      home.username = "yanlin";
+      home.homeDirectory = "/Users/yanlin";
+      home.stateVersion = "24.05";
+
+      home.packages = with pkgs; [
+        texlive.combined.scheme-full
+        btop
+        python312
+        python312Packages.pip
+        python312Packages.virtualenv
+        lftp
+        claude-code.packages.aarch64-darwin.claude-code
+        nerd-fonts.fira-code
+        nerd-fonts.jetbrains-mono
+      ];
+
+      fonts.fontconfig.enable = true;
+
+      programs.home-manager.enable = true;
+
+      programs.zsh = {
+        enable = true;
+        defaultKeymap = "viins";
+        enableVteIntegration = true;
+      };
+    };
+  in
+  {
+    darwinConfigurations."iMac" = nix-darwin.lib.darwinSystem {
+      modules = [ configuration ];
+    };
+
+    homeConfigurations.yanlin = home-manager.lib.homeManagerConfiguration {
+      pkgs = nixpkgs.legacyPackages.aarch64-darwin;
+      modules = [ homeConfiguration ];
+      extraSpecialArgs = { inherit claude-code; };
+    };
+  };
+}