Put Archify right-click entries in their own section at the bottom

Explorer and editor-tab context menus: the Archify commands used the
built-in navigation group and were mixed with New File, New Folder and
the rest. They now use a z_archify group, which VS Code sorts last and
separates with a divider.

package.json

@@ -154,29 +154,29 @@
         {
           "command": "archify.newDiagram",
           "when": "explorerResourceIsFolder",
-          "group": "navigation@10"
+          "group": "z_archify@1"
         },
         {
           "command": "archify.showPreview",
           "when": "resourceFilename =~ /(\\.archify|\\.(architecture|workflow|sequence|dataflow|lifecycle)\\.json)$/",
-          "group": "navigation@20"
+          "group": "z_archify@2"
         },
         {
           "command": "archify.renderToHtml",
           "when": "resourceFilename =~ /(\\.archify|\\.(architecture|workflow|sequence|dataflow|lifecycle)\\.json)$/",
-          "group": "navigation@21"
+          "group": "z_archify@3"
         },
         {
           "command": "archify.openHtmlViewer",
           "when": "resourceExtname == .html",
-          "group": "navigation@20"
+          "group": "z_archify@2"
         }
       ],
       "editor/title/context": [
         {
           "command": "archify.showPreview",
           "when": "resourceFilename =~ /(\\.archify|\\.(architecture|workflow|sequence|dataflow|lifecycle)\\.json)$/",
-          "group": "1_open"
+          "group": "z_archify@1"
         }
       ],
       "file/newFile": [