Adds a browser-local (localStorage only, no backend field) toggle in
the per-agent overflow menu's new settings section: whether otherwise-
collapsed <details> rows in the live terminal (long tool-results,
Write/Edit diffs, ...) default open. Message-bearing rows that already
default open (send/ask/answer/recv) are unaffected either way.
The shared terminal factory (frontend/packages/shared/src/terminal/terminal.js)
gains an optional expandDetails option (boolean or zero-arg function),
read live on every details()/detailsDiff() call rather than captured
once, so flipping the toggle mid-session applies to the next rendered
row without a reload. Unused by the dashboard's own terminal pane, so
its default-closed behaviour is unchanged.
Closes#2961.
198db326b3