fix: apply RTL direction class in the page editor

The reader view (themes/default/components/page.vue) sets `is-rtl`/`is-ltr` on
the root `v-app` from `$vuetify.rtl`, so all `.is-rtl` content styles apply to
rendered pages. The editor's root `v-app` (components/editor.vue) was missing
this class, so for RTL the CKEditor "Visual" editor rendered content
left-to-right, so list bullets stayed on the left. I copied the reader's
binding so the editor inherits the same `.is-rtl` content rules.

client/components/editor.vue

@@ -1,5 +1,5 @@
 <template lang="pug">
-  v-app.editor(:dark='$vuetify.theme.dark')
+  v-app.editor(:dark='$vuetify.theme.dark', :class='$vuetify.rtl ? `is-rtl` : `is-ltr`')
     nav-header(dense)
       template(slot='mid')
         v-text-field.editor-title-input(