fn band_lines(band: &BandState) -> Vec<Line<'static>>Expand description
Build the 4-line display for a band panel:
- Frequency (bold white, MHz with 6 decimal places)
- Mode + Power + Squelch + RX indicator (green “RX” badge when busy)
- S-meter bar (green S0-S3, yellow S5-S7, red S9)
- Step size + ATT indicator (red when attenuator is on)