printedparts stage 12: admin settings page + settings-rail card

PrintedPartsSettings edits the four plugin settings (code prefix,
default threshold, kiosk badge policy, alert recipients) through the
core settings API; the route rides the plugin's router file and the
settings shell nests it into the rail; get_settings_cards contributes
the catalog card while the plugin is enabled.

frontend/src/router/routes/printedparts.js

@@ -31,5 +31,11 @@ export default [
     name: 'printedparts-edit',
     component: () => import('../../views/printedparts/PrintedItemForm.vue'),
     meta: { requiresAuth: true, plugin: 'printedparts' }
+  },
+  {
+    path: 'settings/printedparts',
+    name: 'settings-printedparts',
+    component: () => import('../../views/settings/PrintedPartsSettings.vue'),
+    meta: { requiresAuth: true, requiresAdmin: true, plugin: 'printedparts' }
   }
 ]