fix: place new overlay tracks at the top of the timeline

apps/web/src/lib/timeline/placement/__tests__/resolve.test.ts

@@ -329,7 +329,7 @@ describe("resolveTrackPlacement", () => {
 		).toEqual({
 			kind: "newTrack",
 			trackType: "graphic",
-			insertIndex: 1,
+			insertIndex: 0,
 			insertPosition: null,
 		});
 	});

apps/web/src/lib/timeline/placement/resolve.ts

@@ -176,7 +176,7 @@ export function resolveTrackPlacement({
 		return resolveAlwaysNewTrack({
 			tracks,
 			trackType,
-			position: "default",
+			position: "highest",
 		});
 	}