refactor: KISS cleanup — deduplicate shared config, merge thin files

- Extract fonts, fish.enable, openssh.enable to modules/shared/
- Centralize sshKeys in lib/ via specialArgs
- Merge nixos/base.nix + locale.nix into nixos/default.nix
- Merge home/theme.nix into home/default.nix
- Simplify homeManagerConfig, flake packages output
- Remove redundant vim/wget from NixOS system packages
- Update AGENTS.md to reflect new structure

home/default.nix

@@ -10,9 +10,13 @@
     inputs.catppuccin.homeModules.catppuccin
     ./shell
     ./dev
-    ./theme.nix
   ];
 
+  catppuccin = {
+    enable = true;
+    flavor = "mocha";
+  };
+
   home = {
     username = username;
     homeDirectory = if pkgs.stdenv.isDarwin then "/Users/${username}" else "/home/${username}";
@@ -20,42 +24,37 @@
   };
 
   # ── User-level packages ────────────────────────────
-  home.packages =
-    with pkgs;
-    [
-      # Modern CLI replacements
-      dust # du
-      duf # df
-      procs # ps
-      sd # sed
-      jq # JSON
-      yq # YAML
-      wget
+  home.packages = with pkgs; [
+    # Modern CLI replacements
+    dust # du
+    duf # df
+    procs # ps
+    sd # sed
+    jq # JSON
+    yq # YAML
+    wget
 
-      # System info
-      fastfetch
-      tealdeer # tldr
+    # System info
+    fastfetch
+    tealdeer # tldr
 
-      # File management
-      gomi
+    # File management
+    gomi
 
-      # Nix tools
-      nix-output-monitor # nom
-      nvd # nix version diff
-      nh # nix helper
-      just
+    # Nix tools
+    nix-output-monitor # nom
+    nvd # nix version diff
+    nh # nix helper
+    just
 
-      # Secrets management (WSL uses Windows op.exe via interop)
-    ]
-    ++ (with pkgs; [
-      # AI coding agent
-      opencode
-      comment-checker
+    # AI coding agent
+    opencode
+    comment-checker
 
-      # Misc
-      ffmpeg
-      pandoc
-    ]);
+    # Misc
+    ffmpeg
+    pandoc
+  ];
 
   # XDG directories
   xdg.enable = true;

home/theme.nix

@@ -1,8 +0,0 @@
-{ ... }:
-
-{
-  catppuccin = {
-    enable = true;
-    flavor = "mocha";
-  };
-}