web/device: add global constant for device info

web/src/components/save/buttons/DownloadButton.svelte

@@ -2,15 +2,13 @@
     import '@fontsource-variable/noto-sans-mono';
 
     import API from "$lib/api";
+    import device from '$lib/device';
 
     export let url: string;
 
     $: buttonText = '>>';
     $: isDisabled = false;
 
-    const ua = navigator.userAgent.toLowerCase();
-    const isIOS = ua.includes("iphone os") || (ua.includes("mac os") && navigator.maxTouchPoints > 0);
-
     const changeDownloadButton = (state: string) => {
         isDisabled = true;
         switch(state) {
@@ -37,7 +35,7 @@
     }
 
     const downloadFile = (url: string) => {
-        if (isIOS) {
+        if (device.isIOS) {
             return navigator?.share({ url }).catch(() => {});
         } else {
             return window.open(url, '_blank');