feat(motor-antenna): band selector for the follow filter (replaces min/max range)

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.

frontend/wailsjs/go/models.ts

@@ -3156,6 +3156,7 @@ export namespace main {
 	    follow: boolean;
 	    step_khz: number;
 	    tx_inhibit: boolean;
+	    bands: string[];
 	    freq_min_mhz: number;
 	    freq_max_mhz: number;
 	
@@ -3175,6 +3176,7 @@ export namespace main {
 	        this.follow = source["follow"];
 	        this.step_khz = source["step_khz"];
 	        this.tx_inhibit = source["tx_inhibit"];
+	        this.bands = source["bands"];
 	        this.freq_min_mhz = source["freq_min_mhz"];
 	        this.freq_max_mhz = source["freq_max_mhz"];
 	    }