The BUILD sub-tab description was written before the auto-scroll,
live elapsed-time ticker, and SSE-driven list refresh were added.
Update it to cover:
- Live elapsed-time chip: ticks every second via setInterval,
cleared on finish/error
- Sticky-bottom auto-scroll: follows new output while the operator
is at the bottom; silently appends when scrolled up
- SSE-driven list refresh: rebuild_queue_changed fires a 2s-debounced
fetchBuild() while on the BUILD tab; refresh button still works for
immediate re-fetch
c70823755b