Trubo: Login callback CSRF/session fixation

### Impact Turborepo's self-hosted login and SSO browser flows did not validate a CSRF state value on the localhost callback. While the CLI was waiting for authentication, a malicious web page could send a request to the local callback server with an attacker-controlled token. If accepted before the legitimate callback, the CLI could complete login with the wrong credentials. This affects users authenticating the `turbo` CLI against self-hosted remote cache/auth endpoints. Vercel-hosted login flows using device authorization are not affected. ### Fix The login and SSO redirect flows now generate a random state value, include it in the browser authentication URL, and require the same value on the localhost callback before accepting a token. Callbacks with a missing or mismatched state are rejected. ### Workarounds If you cannot upgrade immediately, avoid browser-based self-hosted `turbo login` or SSO flows on machines that may load untrusted web content during authentication. Use a pre-provisioned token or environment-based authentication instead.