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/src/components/SettingsModal.tsx

@@ -1055,8 +1055,8 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
   const [rotatorTest, setRotatorTest] = useState<{ ok: boolean; msg: string } | null>(null);
 
   // Motorized antenna (Ultrabeam TCP or SteppIR TCP/serial) settings.
-  const [ultrabeam, setUltrabeam] = useState<{ enabled: boolean; type: string; transport: string; host: string; port: number; com: string; baud: number; follow: boolean; step_khz: number; tx_inhibit: boolean }>({
-    enabled: false, type: 'ultrabeam', transport: 'tcp', host: '', port: 23, com: '', baud: 9600, follow: false, step_khz: 50, tx_inhibit: false,
+  const [ultrabeam, setUltrabeam] = useState<{ enabled: boolean; type: string; transport: string; host: string; port: number; com: string; baud: number; follow: boolean; step_khz: number; tx_inhibit: boolean; freq_min_mhz: number; freq_max_mhz: number }>({
+    enabled: false, type: 'ultrabeam', transport: 'tcp', host: '', port: 23, com: '', baud: 9600, follow: false, step_khz: 50, tx_inhibit: false, freq_min_mhz: 13, freq_max_mhz: 54,
   });
   const [ubTesting, setUbTesting] = useState(false);
   const [ubTest, setUbTest] = useState<{ ok: boolean; msg: string } | null>(null);
@@ -2639,6 +2639,22 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
               </div>
             )}
           </div>
+          {isSteppir && (
+            <div className="border-t border-border/60 pt-3 space-y-1">
+              <div className="flex items-center gap-2 flex-wrap">
+                <Label className="text-sm">{t('hw.steppirRange')}</Label>
+                <input type="number" min={1} max={60} value={ultrabeam.freq_min_mhz}
+                  onChange={(e) => setUltrabeam((s) => ({ ...s, freq_min_mhz: parseInt(e.target.value, 10) || 0 }))}
+                  className="h-8 w-16 rounded-md border border-input bg-background px-2 text-sm" />
+                <span className="text-xs text-muted-foreground">–</span>
+                <input type="number" min={1} max={60} value={ultrabeam.freq_max_mhz}
+                  onChange={(e) => setUltrabeam((s) => ({ ...s, freq_max_mhz: parseInt(e.target.value, 10) || 0 }))}
+                  className="h-8 w-16 rounded-md border border-input bg-background px-2 text-sm" />
+                <span className="text-xs text-muted-foreground">MHz</span>
+              </div>
+              <p className="text-xs text-muted-foreground">{t('hw.steppirRangeHint')}</p>
+            </div>
+          )}
           <div className="border-t border-border/60 pt-3 space-y-1">
             <label className="flex items-center gap-2 text-sm cursor-pointer">
               <Checkbox checked={ultrabeam.tx_inhibit} onCheckedChange={(c) => setUltrabeam((s) => ({ ...s, tx_inhibit: !!c }))} />