Add Arduino support, dialout group, and Zed skill

- Enable the Arduino IDE flatpak and add it to the system modules list.

- Add the user to the `dialout` group for serial device access.
- Include a new Zed skill configuration that fetches a remote skill
  file.

modules/home/zed/default.nix

@@ -19,5 +19,6 @@
     ./user-settings
     ./extensions.nix
     ./extra-packages.nix
+    ./skills.nix
   ];
 }

modules/home/zed/skills.nix

@@ -0,0 +1,20 @@
+{
+  pkgs,
+  # lib,
+  ...
+}: let
+  skillPath = ".agents/skills";
+  urlDomain = "https://raw.githubusercontent.com";
+  refs = "refs/heads/main/skills";
+in {
+  home.file = {
+    "${skillPath}/ponytail/SKILL.md".source = pkgs.fetchurl {
+      url = "${urlDomain}/DietrichGebert/ponytail/${refs}/ponytail/SKILL.md";
+      sha256 = "sha256-IiTh4N3bHhJtER4HYPEFEo1g9Ro703TiPA5Tigv7k3s=";
+    };
+    "${skillPath}/caveman/SKILL.md".source = pkgs.fetchurl {
+      url = "${urlDomain}/JuliusBrussee/caveman/${refs}/caveman/SKILL.md";
+      sha256 = "sha256-447Gcey+5HziNBkL4SYV2vYKxmfXdbc0DUnQf09jx7w=";
+    };
+  };
+}