A contiguous FreqMin/FreqMax range can't drop a single band while keeping its
neighbours — so it couldn't express "40 m and 20 m yes, 30 m no" for an antenna
whose 30 m extension isn't fitted. Replace it with a Covered bands selector
(40 m–6 m) that applies to both the Ultrabeam and the SteppIR.
The follow loop and immediate re-tune now gate on band membership
(motorBandAllowed) instead of a MHz range: only bands in the operator's set are
followed, and 80 m/160 m are never followed (outside a beam's reach) regardless.
The legacy FreqMin/FreqMax is migrated to a band set on load and still
round-trips, so existing configs are unchanged. UI swaps the two number inputs
for a row of toggle chips.