Three UX improvements for the live build log viewer:
1. Auto-scroll (sticky-bottom): live build output now scrolls to the
bottom as new lines arrive. Stops auto-scrolling when the operator
manually scrolls up; resumes when they scroll back to the bottom.
Same intent-tracking pattern used by the terminal pane.
2. Elapsed-time ticker: running builds show a live seconds/minutes
counter in the row header that ticks every second. Stops and shows
the final duration when the build finishes (done frame received)
or errors out.
3. SSE-driven list refresh: subscribes to /dashboard/stream and
debounces a fetchBuild() call (2s) whenever rebuild_queue_changed
fires while the BUILD tab is active. New log entries and status
changes appear without a manual refresh.
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