
`/users/:user`, `/@:user`, `/notes/:note` return different responses depending on the request's `Accept:` header. If we don't consistently return a `Vary: Accept` header, browsers and caching proxies will get confused, and return AP representations when HTML was requested, or vice versa. Co-authored-by: dakkar <dakkar@thenautilus.net> Co-authored-by: syuilo <Syuilotan@yahoo.co.jp>