PathCompute.compute/5 now accepts an :on_progress callback and emits
9 named stages (resolve → terrain → HRRR grid → atmospheric → sounding
→ scoring → budget → forecast → ionosphere). PathLive runs the compute
in start_async, streams {:compute_progress, step, total, label}
messages from the callback, and renders the current stage + step/total
in the disabled button alongside a daisyUI progress bar — replacing
the static "Computing..." while the multi-second pipeline runs.
handle_async covers :ok, :error, and {:exit, _} (last logs per the
CLAUDE.md async-error rule). Existing PathLive tests that asserted on
result content after live() were switched to render_async(lv) so they
wait for the task; new tests cover the progress callback ordering and
the in-flight label rendering.