add not-found handling to ZK and hotlink viewer pages.

Rename ViewerView and view store to ZkViewerView and useZkViewStore; unify hotlink load and ZK unlock error copy.

frontend/src/stores/zkView.ts

@@ -7,7 +7,7 @@ import { toArrayBuffer } from '@/utils/toArrayBuffer';
 import { decryptPasswordProtectedZkUpload } from '@/utils/upload/decryptPasswordProtectedZkUpload';
 import { decryptZkUpload } from '@/utils/upload/decryptZkUpload';
 
-export const useViewStore = defineStore('view', () => {
+export const useZkViewStore = defineStore('zkView', () => {
     const imageObjectUrl = ref<string | null>(null);
 
     const clearImage = (): void => {