frontend: attach auth credentials to all API requests

Add Authorization Bearer header to all fetch calls (apps, stream
start). Handle 401 responses by clearing token and redirecting to
login. Pass stream_token from the stream start response through to
the WebTransport URL as a query parameter for proxy authentication.

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

frontend/src/routes/stream/Stream.svelte

@@ -8,17 +8,20 @@
 		certHash: Array<number>;
 		width: number;
 		height: number;
+		streamToken: string;
 	}
 
-	let { url, certHash, width, height }: Props = $props();
+	let { url, certHash, width, height, streamToken }: Props = $props();
 	let loading = $state(true);
 	let fullscreen = $state(false);
 	let gameplayView: HTMLDivElement;
 	let gameplayCanvas: HTMLCanvasElement;
 
 	async function startStream() {
+		// Append stream token to URL for proxy authentication
+		const authenticatedUrl = url + (url.includes('?') ? '&' : '?') + 'token=' + encodeURIComponent(streamToken);
 		await startWebtransportStream(
-			url,
+			authenticatedUrl,
 			certHash,
 			width,
 			height,