Shared Spinner component for button loading states

Adds a reusable shadcn-style Spinner (lucide loader-circle icon,
localized aria-label) and wires it into every button that has a
pending state: comment submit, delete, tag save, profile save,
admin saves, upload, login and register.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/pages/admin.vue

@@ -15,6 +15,7 @@ import {
   SelectTrigger,
   SelectValue,
 } from '@/components/ui/select'
+import { Spinner } from '@/components/ui/spinner'
 import { Textarea } from '@/components/ui/textarea'
 
 definePageMeta({ middleware: 'admin' })
@@ -219,6 +220,7 @@ async function saveMotd() {
                 :disabled="savingRole === role.id"
                 @click="savePermissions(role)"
               >
+                <Spinner v-if="savingRole === role.id" />
                 {{ savingRole === role.id ? $t('common.saving') : $t('common.save') }}
               </Button>
               <Button
@@ -323,6 +325,7 @@ async function saveMotd() {
             class="min-h-16"
           />
           <Button type="submit" class="shrink-0" :disabled="motdSaving">
+            <Spinner v-if="motdSaving" />
             {{ motdSaving ? $t('common.saving') : $t('common.save') }}
           </Button>
         </form>