Show on /weather where the detected duct geometry traps each microwave
band. Overview mode bins cells by their lowest trapped frequency
(Bean & Dutton cutoff); band-picker mode masks cells whose duct doesn't
reach the selected band. Cutoff is pre-computed per cell in both
writers (Elixir derive + Rust derive_row reads best_duct_freq_ghz from
CellValues), persisted to ScalarFile, and shipped to the JS hook via
the existing binary cell pack. Also cleans up six pre-existing
length/1 credo warnings in unrelated test files.
Graham McIntire
e3d430f8c4