In the single-line (focused) message-list layout, the subject span used
`shrink-0`, which prevented `truncate` from engaging: a long subject sized to
its full content width and overflowed the bounded subject/preview group,
rendering on top of the timestamp on the right.
Let the subject shrink and truncate (`shrink-0` -> `min-w-0`), and give the
inline preview a high shrink factor (`shrink-[9999]`) so it collapses first —
the subject stays fully visible while there's room and only truncates with an
ellipsis once the preview is gone, never colliding with the time.
Applied to both email-list-item and thread-list-item (single-email and
thread-aggregate rows).
