feat(webui): quality of life improvements for upload dialog

- when uploading, warn before closing tab
- allow cancelling in progress uploads
- when uploading multiple files, scroll to the current file

webui/src/lib/components/AddModal.svelte

@@ -21,10 +21,13 @@
 	let files: File[] = [];
 	let URLs: string[] = [];
 	let uploading = false;
+	let abortController: AbortController | undefined;
 
 	let progress: Record<string, number> = {};
 	let totalProgress: number | undefined;
 
+	let filesElement: HTMLDivElement;
+
 	$: visible = files.length + URLs.length > 0;
 
 	addEmitter.on('files', (ev) => {
@@ -40,9 +43,15 @@
 		uploading = true;
 
 		try {
+			abortController = new AbortController();
 			const addresses: string[] = [];
-			for (const file of files) {
+			for (const [idx, file] of files.entries()) {
+				filesElement
+					?.querySelectorAll('.entry')
+					[idx]?.scrollIntoView({ behavior: 'smooth', block: 'center' });
+
 				const address = await api.putBlob(file, {
+					abortController,
 					onProgress: (p) => {
 						progress[file.name] = (p.loaded / p.total) * 100;
 						totalProgress = Object.values(progress).reduce((a, b) => a + b, 0) / files.length;
@@ -50,6 +59,10 @@
 					timeout: -1
 				});
 				addresses.push(address);
+
+				if (!uploading) {
+					break;
+				}
 			}
 
 			if (addresses.length == 1) {
@@ -67,11 +80,16 @@
 	}
 
 	function reset() {
-		if (!uploading) {
-			files = [];
-			URLs = [];
-			progress = {};
+		if (uploading) {
+			const msg = $i18n.t('Are you sure you want to cancel the upload?');
+			if (!confirm(msg)) return;
 		}
+		abortController?.abort();
+
+		files = [];
+		URLs = [];
+		progress = {};
+		uploading = false;
 	}
 
 	function onKeydown(event: KeyboardEvent) {
@@ -84,14 +102,22 @@
 			reset();
 		}
 	}
+
+	function onBeforeUnload(ev: BeforeUnloadEvent) {
+		if (files.length || uploading) {
+			ev.preventDefault();
+			ev.returnValue = true;
+		}
+	}
 </script>
 
+<svelte:window on:beforeunload={onBeforeUnload} />
 <svelte:body on:keydown={onKeydown} />
 
 <!-- svelte-ignore a11y-click-events-have-key-events a11y-no-static-element-interactions -->
 <div class="addmodal-container" class:visible class:uploading on:click={reset}>
 	<div class="addmodal" on:click|stopPropagation>
-		<div class="files">
+		<div class="files" bind:this={filesElement}>
 			{#each files as file}
 				<div class="entry">
 					<div class="row">