<timeline-entry>

One event on a timeline-container: a dot on the vertical line, an optional
headline, a relative timestamp ("3 hours ago"), and freely nested content.
The connecting line is drawn here — its segment above the dot is hidden on
the first entry and the segment below is hidden on the last, so the line caps
exactly at the first and last dots. Only meaningful inside a
timeline-container; demonstrated through it.

datetime is the entry's one timestamp. A nested element that has its own
timestamp prop (e.g. chat-message's timestamp) should leave it unset —
setting both renders the same time twice.

label is a free-text alternative for a timeline whose axis is not a wall
clock — a year, an era, a phase. It wins over datetime when both are set.
Slot label instead when it needs its own styling, since a property is
rendered inside this component's shadow DOM and cannot be reached from
outside.

alternating is set by timeline-container and should not be set by hand:
it switches the entry to three columns — label, line, body — with the sides
swapping on every second entry. The entry fills whatever height it is given,
so the line spans it rather than only its content — do not override the
host's display from outside, since a light-DOM rule beats the :host
declaration this relies on.

The dot's color types the entry using the shared status-pill palette —
primary by default, plus neutral, info, success, warning, and
danger.

Set compact for dense, one-line system-status entries: it tightens the
vertical spacing and renders the content smaller and muted.

Set running to replace the dot with an animated gray ring spinner,
indicating the entry represents in-progress work; color has no visible
effect while running is set.