fix(ui): mount ImageViewer globally so tile clicks open as overlay, not route-redirect to /gallery

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

frontend/src/App.vue

@@ -3,6 +3,7 @@
     <AppShell>
       <RouterView />
     </AppShell>
+    <ImageViewer v-if="modal.isOpen" @close="modal.close()" />
     <AppSnackbar ref="snackbar" />
   </v-app>
 </template>
@@ -11,7 +12,10 @@
 import { onMounted, ref } from 'vue'
 import AppShell from './components/AppShell.vue'
 import AppSnackbar from './components/AppSnackbar.vue'
+import ImageViewer from './components/modal/ImageViewer.vue'
+import { useModalStore } from './stores/modal.js'
 
+const modal = useModalStore()
 const snackbar = ref(null)
 
 onMounted(() => {