feat(nav): teleport Showcase Shuffle into the nav action slot

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/views/ShowcaseView.vue

@@ -1,11 +1,11 @@
 <template>
   <v-container fluid class="py-6">
-    <div class="fc-showcase__head">
+    <Teleport to="#fc-nav-actions">
       <v-btn
         prepend-icon="mdi-shuffle-variant" variant="tonal" color="accent"
-        :loading="store.loading" @click="store.shuffle()"
+        size="small" :loading="store.loading" @click="store.shuffle()"
       >Shuffle</v-btn>
-    </div>
+    </Teleport>
 
     <v-alert v-if="store.error" type="error" variant="tonal" closable class="my-4">
       Failed to load: {{ store.error }}
@@ -39,10 +39,3 @@ function openImage(id) {
   router.push({ name: 'gallery', query: { image: id } })
 }
 </script>
-
-<style scoped>
-.fc-showcase__head {
-  display: flex; align-items: center; justify-content: flex-end;
-  margin-bottom: 16px;
-}
-</style>