#6953 fix(app): allow static segments as siblings of dynamic route segments

_find_route_conflict flagged a conflict whenever an existing route's dynamic segment lined up with a different static segment of a new bracket-containing route (e.g. /posts/[id] vs /posts/all/[x]), and only in that registration order. React Router resolves such siblings fine (static wins), so only two dynamic segments with different names at the same position are a real conflict.