fix: vertically center first install (#3501)

lnbits/templates/pages/first-install.vue

@@ -1,4 +1,5 @@
 <template id="page-first-install">
+  <div class="fullscreen">
     <div class="row q-col-gutter-md justify-center main first-install">
       <div class="col-10 col-md-8 col-lg-6 q-gutter-y-md">
         <q-card>
@@ -40,7 +41,8 @@
                   :rules="[
                     val => !val || val.length >= 8 || $t('invalid_password'),
                     val =>
-                    val === loginData.password || $t('invalid_password_repeat')
+                      val === loginData.password ||
+                      $t('invalid_password_repeat')
                   ]"
                   ><template v-slot:append>
                     <q-icon
@@ -72,4 +74,5 @@
         </q-card>
       </div>
     </div>
+  </div>
 </template>