v0.159.0

A lapsed sign-in falls back to Sonnet 5 (#302). A reader whose token had expired was refused with «You are signed out; sign in again with /login.» and the question stayed unsent. Now the chat forgets the sign-in, says in one dim line «Your sign-in has expired, so Sonnet 5 answers now. Sign in again with /login to choose a model.» (German: «Deine Anmeldung ist abgelaufen, darum antwortet jetzt Sonnet 5. Melde dich mit /login wieder an, um ein Modell zu wählen.»), and sends the question as a visitor's, which Sonnet 5 answers. A signed_out from the chat host does the same and sends the question again at once without the token. A canceled /login still says the reader is signed out.

What breaks. Nothing. A signed-in reader whose token holds sees no change.

How to take it. Re-pin and run npm run design; chat.js is what changes.

Verified: npm test (1114 pass, Playwright included) and conventions-check pass on the release commit.