fix: stats position adjusts when queue opens/closes (#426)

The platform stats in the header were positioned using a static viewport
calculation that didn't account for the queue sidebar width. Now uses a
CSS custom property (--queue-width) that gets updated dynamically when
the queue visibility changes, ensuring the stats shift left along with
the rest of the header content.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <[e-mail]>

frontend/src/lib/components/Header.svelte

···
 
 	.stats-left {
 		position: absolute;
-		left: calc((100vw - 800px) / 4);
+		left: calc((100vw - var(--queue-width, 0px) - 800px) / 4);
 		top: 50%;
 		transform: translate(-50%, -50%);
+		transition: left 0.3s ease;
 	}
 
 	.bluesky-link,

frontend/src/routes/+layout.svelte

···
 		updateTitle();
 	});
 
+	// set CSS custom property for queue width adjustment
+	$effect(() => {
+		if (!browser) return;
+		const queueWidth = showQueue && !isEmbed ? '360px' : '0px';
+		document.documentElement.style.setProperty('--queue-width', queueWidth);
+	});
+
 	function handleQueueShortcut(event: KeyboardEvent) {
 		// ignore modifier keys
 		if (event.metaKey || event.ctrlKey || event.altKey) {
···
 	}
 
 	:global(:root) {
+		/* layout */
+		--queue-width: 0px;
+
 		/* accent colors - configurable */
 		--accent: #6a9fff;
 		--accent-hover: #8ab3ff;