player breakpoint improvements

src/lib/components/GlobalPlayer.svelte

@@ -67,9 +67,24 @@
 
 	let unsubscribe: (() => void) | null = null;
 
+	// Track breakpoint transitions so we can auto open/close on crossing:
+	// - desktop -> mobile: auto close
+	// - mobile -> desktop: auto open
+	let prevIsMobile: boolean | null = $state(null);
+
 	function updateIsMobile() {
-		if (!browser) return;
-		isMobile = window.matchMedia?.("(max-width: 1023px)")?.matches ?? false;
+		const nextIsMobile =
+			window.matchMedia?.("(max-width: 1023px)")?.matches ?? false;
+
+		// Update local derived flag
+		isMobile = nextIsMobile;
+
+		// On transitions, sync player UI open state
+		if (prevIsMobile !== null && prevIsMobile !== nextIsMobile) {
+			setUiOpen(!nextIsMobile);
+		}
+
+		prevIsMobile = nextIsMobile;
 	}
 
 	// Media Session bindings