refactor: 重构为多平台多用户架构，全面提升终端体验

- 新增 lib/ 辅助函数（mkNixos/mkDarwin/mkHome），消除硬编码
- 拆分 modules/ 为 nixos/darwin/shared 三层，支持跨平台共享
- 重构 home/ 为 shell/dev/theme 子模块，工具全部迁入用户级
- 深度配置 Tmux/FZF/Atuin/Bat/Eza/Btop/Lazygit/Starship
- 添加 Catppuccin Mocha 统一主题、Nerd Fonts 声明式管理
- 新增 homeConfigurations 输出，支持非 NixOS 系统直装
- 新增 nix-darwin 输入，预留 macOS 扩展路径
- 新增 overlays/ 和 pkgs/ 自定义包基础设施
- 修正 nix-darwin URL（LnL7 → nix-darwin org）

home/default.nix

@@ -1,16 +1,56 @@
-{ config, pkgs, ... }:
+{
+  inputs,
+  username,
+  pkgs,
+  lib,
+  ...
+}:
 
 {
   imports = [
-    ./shell.nix
-    ./git.nix
+    inputs.catppuccin.homeManagerModules.catppuccin
+    ./shell
+    ./dev
+    ./theme.nix
   ];
 
-  home.stateVersion = "24.11";
+  home = {
+    username = username;
+    homeDirectory =
+      if pkgs.stdenv.isDarwin then "/Users/${username}" else "/home/${username}";
+    stateVersion = "24.11";
+  };
 
-  # ── mise 配置 ──
-  xdg.configFile."mise/config.toml".text = ''
-    [settings]
-    trusted_config_paths = ["/"]
-  '';
+  # ── User-level packages ────────────────────────────
+  home.packages = with pkgs; [
+    # Modern CLI replacements
+    dust # du
+    duf # df
+    procs # ps
+    sd # sed
+    xh # curl/httpie
+    jq # JSON
+    yq # YAML
+
+    # System info
+    fastfetch
+    tealdeer # tldr
+
+    # File management
+    trash-cli
+
+    # Terminal multiplexer (alternative)
+    zellij
+
+    # Nix tools
+    nix-output-monitor # nom — better nix build output
+    nvd # nix version diff
+    nh # nix helper (nixos-rebuild wrapper)
+
+    # Misc
+    micro # simple editor fallback
+  ];
+
+  # XDG directories
+  xdg.enable = true;
 }