feat: configurable SteppIR tunable range — skip follow/inhibit off-band

A SteppIR only covers part of the spectrum (a standard one is 20 m–6 m) but
can't report its own range, so the follow loop's existing out-of-range guard
(FreqMin/FreqMax) never engaged for it. Tuning the rig to a band the antenna
can't reach (e.g. 30 m) made the loop keep trying — the immediate cause of the
stuck TX interlock addressed in the previous commit.

Add a Tunable range (MHz) setting to the Antenna panel, wired into the SteppIR
adapter's Status().FreqMin/FreqMax so the follow loop skips out-of-range
frequencies entirely: no tune command, no TX inhibit. Defaults to 13–54 MHz
(20 m–6 m, the common model) when unset; widen the low edge for a 40 m-equipped
SteppIR. Ultrabeam is unaffected (it reports its own per-band coverage).

Keeps the last-commanded-freq deadband from the previous commit as a universal
safety net for any flaky-status case within the valid range.

frontend/wailsjs/go/models.ts

@@ -2960,6 +2960,8 @@ export namespace main {
 	    follow: boolean;
 	    step_khz: number;
 	    tx_inhibit: boolean;
+	    freq_min_mhz: number;
+	    freq_max_mhz: number;
 	
 	    static createFrom(source: any = {}) {
 	        return new UltrabeamSettings(source);
@@ -2977,6 +2979,8 @@ export namespace main {
 	        this.follow = source["follow"];
 	        this.step_khz = source["step_khz"];
 	        this.tx_inhibit = source["tx_inhibit"];
+	        this.freq_min_mhz = source["freq_min_mhz"];
+	        this.freq_max_mhz = source["freq_max_mhz"];
 	    }
 	}
 	export class UltrabeamStatusInfo {