Improve ZK and hotlink viewer image layout and add open-full-image link.

Share ViewerImageDisplay with viewport-aware sizing so wide panoramas are not capped at max-w-lg.

frontend/src/views/ZkViewerView.vue

@@ -1,7 +1,5 @@
 <template>
-    <main
-        class="mx-auto flex w-full max-w-lg flex-1 flex-col items-center justify-center gap-3 px-4 py-6 text-center sm:px-6 sm:py-8"
-    >
+    <main class="flex min-h-0 w-full flex-1 flex-col items-center justify-center px-4 py-4 sm:px-6">
         <p v-if="state === 'loading'" class="text-sm text-muted-foreground sm:text-base">Loading image...</p>
 
         <p v-else-if="state === 'invalidLink'" class="text-sm text-muted-foreground">
@@ -37,10 +35,9 @@
             </button>
         </form>
 
-        <img
+        <ViewerImageDisplay
             v-else-if="state === 'image' && imageObjectUrl"
             :src="imageObjectUrl"
-            class="max-h-[min(80vh,100dvh)] w-full object-contain"
         />
     </main>
 </template>