fix: resolve Svelte a11y and reactivity build warnings

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

src/routes/fitness/[workout=fitnessWorkout]/[active=fitnessActive]/+page.svelte

@@ -90,7 +90,7 @@
 		}
 	}
 
-	let gpsToggling = false;
+	let gpsToggling = $state(false);
 	async function toggleGps() {
 		if (gpsToggling) return;
 		gpsToggling = true;