Replaces the "tropo composite + post-hoc aurora boost" model with a
max-over-mechanisms dispatcher so each band's score reflects the
dominant propagation channel rather than summing alternative paths.
- BandConfig.mechanisms/1 derives the stack from frequency:
≤432 MHz gets [:tropo, :aurora]; >432 MHz stays [:tropo]. Bands
may override with an explicit :mechanisms field.
- Scorer.mechanism_score/3 returns a standalone integer score for
one mechanism (:tropo delegates to composite_score; :aurora is a
clean Kp/freq function, not a boost on top of tropo).
- Scorer.cell_score/2 takes max across the band's mechanisms so a
Kp-6 storm scores 6m at 85 even when the tropo picture is poor,
instead of conflating the two channels.
Es and F2 stay in PathCompute since they're path-distance-dependent.
The legacy aurora_boost path is unchanged so no callers shift today.
Graham McIntire
a68027b00b