fix(adguard): add newline before filtering section

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

modules/adguard.nix

@@ -97,8 +97,7 @@ in
           querylog_enabled: true
           querylog_file_enabled: true
           statistics_enabled: true
-        ''
-        + lib.optionalString (cfg.clients != []) ''
+        '' + lib.optionalString (cfg.clients != []) ''
           clients:
             persistent:
               ${lib.concatStringsSep "\n              " (
@@ -108,6 +107,7 @@ in
                       - ${config.sops.placeholder.${client.idSecret}}
                 '') cfg.clients
               )}
+        '' + ''
 
         filtering:
           protection_enabled: true