DRY pass #3: one compact dialog button (#5373)

ShareDialog's Share and NoteEditor's Add note / Close each spelled out the
same compact button, smaller than .btn. .btn-compact is its shape and
.btn-compact-primary its brand fill; Close keeps its neutral colours beside it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/components/NoteEditor.vue

@@ -822,10 +822,11 @@ function revPreview(rev: NoteRevision): string {
           </NoteActions>
           <button
             type="button"
+            class="btn-compact"
             :class="
               isCreate
-                ? 'rounded-md bg-brand px-3 py-1.5 text-sm font-semibold text-neutral-900 hover:brightness-95 focus:outline-none focus-visible:ring-2 focus-visible:ring-brand disabled:opacity-60'
-                : 'rounded-md px-3 py-1.5 text-sm font-semibold text-neutral-700 hover:bg-neutral-100 focus:outline-none focus-visible:ring-2 focus-visible:ring-brand disabled:opacity-60 dark:text-neutral-200 dark:hover:bg-neutral-800'
+                ? 'btn-compact-primary'
+                : 'text-neutral-700 hover:bg-neutral-100 dark:text-neutral-200 dark:hover:bg-neutral-800'
             "
             :disabled="saving"
             @click="close()"