add radicle-explorer module, and enable it on Cape

nixos/modules/programs/caddy/default.nix

@@ -0,0 +1,28 @@
+{
+  lib,
+  config,
+  ...
+}: let
+  cfg = config.youthlic.programs.caddy;
+in {
+  imports = [
+    ./radicle-explorer.nix
+  ];
+  options = {
+    youthlic.programs.caddy = {
+      enable = lib.mkEnableOption "caddy";
+      baseDomain = lib.mkOption {
+        type = lib.types.str;
+        example = "youthlic.fun";
+      };
+    };
+  };
+  config = lib.mkIf cfg.enable {
+    services.caddy = {
+      enable = true;
+    };
+    networking.firewall = {
+      allowedTCPPorts = [443];
+    };
+  };
+}