Add modular service configuration with SearXNG and Nginx

- Create modules/ directory with reusable NixOS modules
- Add system module for main user configuration
- Add podman module for rootless container support
- Add nginx module with automatic Let's Encrypt SSL
- Add searxng module with Anubis AI firewall protection
- Configure SearXNG at search.ashisgreat.xyz
- Enable nginx reverse proxy with HTTPS

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

modules/system.nix

@@ -0,0 +1,25 @@
+# System Module
+# Provides: Common system configuration options used by other modules
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+let
+  cfg = config.myModules.system;
+in
+{
+  options.myModules.system = {
+    mainUser = lib.mkOption {
+      type = lib.types.str;
+      default = "ashie";
+      description = "Main user account for running services";
+    };
+  };
+
+  config = {
+    # Nothing here by default - just provides the option
+  };
+}