feat(upload): show progress bar in drop zone during upload

Replaces fetch with XMLHttpRequest to get upload progress events.
The drop zone shows a filling progress bar and percentage while
files are uploading, then reverts to the normal hint when done.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/+page.svelte

@@ -25,6 +25,7 @@ let isDragging = $state(false);
 let windowDragging = $state(false);
 let dragCounter = 0;
 let isUploading = $state(false);
+let uploadProgress = $state(0);
 let uploadMessages = $state<{ text: string; isError: boolean; link?: string }[]>([]);
 let fileInput: HTMLInputElement;
 
@@ -85,19 +86,26 @@ async function uploadFiles(files: File[]) {
 	}
 
 	isUploading = true;
+	uploadProgress = 0;
 	try {
 		const formData = new FormData();
 		for (const file of valid) {
 			formData.append('files', file);
 		}
 
-		const res = await fetch('/api/documents/quick-upload', {
-			method: 'POST',
-			body: formData
+		const { ok, body } = await new Promise<{ ok: boolean; body: string }>((resolve, reject) => {
+			const xhr = new XMLHttpRequest();
+			xhr.open('POST', '/api/documents/quick-upload');
+			xhr.upload.addEventListener('progress', (e) => {
+				if (e.lengthComputable) uploadProgress = Math.round((e.loaded / e.total) * 100);
+			});
+			xhr.addEventListener('load', () => resolve({ ok: xhr.status < 300, body: xhr.responseText }));
+			xhr.addEventListener('error', () => reject(new Error('Network error')));
+			xhr.send(formData);
 		});
 
-		if (res.ok) {
-			const result = await res.json();
+		if (ok) {
+			const result = JSON.parse(body);
 			if (result.created?.length > 0) {
 				messages.push({ text: m.upload_success({ count: result.created.length }), isError: false });
 			}
@@ -122,6 +130,7 @@ async function uploadFiles(files: File[]) {
 		}
 	} finally {
 		isUploading = false;
+		uploadProgress = 0;
 		uploadMessages = messages;
 	}
 }
@@ -372,10 +381,20 @@ $effect(() => {
 				<polyline points="17 8 12 3 7 8" />
 				<line x1="12" y1="3" x2="12" y2="15" />
 			</svg>
-			<span class="font-sans font-medium">
-				{isUploading ? '…' : m.upload_drop_hint()}
-			</span>
-			<span class="font-sans text-xs text-ink-3">{m.upload_accepted_types()}</span>
+			{#if isUploading}
+				<div class="flex w-48 flex-col items-center gap-1">
+					<div class="h-1.5 w-full overflow-hidden rounded-full bg-ink/10">
+						<div
+							class="h-full rounded-full bg-primary transition-all duration-200"
+							style="width: {uploadProgress}%"
+						></div>
+					</div>
+					<span class="font-sans text-xs text-ink-3">{uploadProgress}%</span>
+				</div>
+			{:else}
+				<span class="font-sans font-medium">{m.upload_drop_hint()}</span>
+				<span class="font-sans text-xs text-ink-3">{m.upload_accepted_types()}</span>
+			{/if}
 		</div>
 
 		{#if uploadMessages.length > 0}