Add a keyNav prop to BandMap: when set (only the docked Main-view map, not the
multi-band Band Map tab), Ctrl+ArrowUp / Ctrl+ArrowDown selects the next in-band
spot above / below the rig frequency and tunes to it via the existing spot-click
handler. Higher freq is up on the map (freqToY), so Up = next higher spot.
Ignored while typing in an input. Changelog 0.21.1.