feat: Denkovi USB 8-relay board (FT245 D2XX bit-bang)

Third relay device alongside WebSwitch and KMTronic. Despite enumerating as a
COM port, this board is driven via FTDI D2XX synchronous bit-bang (one byte = 8
relays, bit 0 = relay 1), not serial ASCII — so we load ftd2xx.dll at runtime
(no CGO) and call FT_OpenEx/FT_SetBitMode/FT_Write, addressing the board by its
FTDI serial (e.g. DAE0006K), exactly like the vendor tool. Windows-only (stub
elsewhere); ListDenkoviDevices enumerates connected serials for the picker.

Wired into relaydev (Count/Status/Set), app.go (deviceDriver/relayCountFor/type
whitelist + ListDenkoviDevices binding), and the Station device editor (new type
+ FTDI-serial field with Detect). Untested on hardware; bit order / on-polarity
may need a flip after a live test.

frontend/src/components/StationControlPanel.tsx

@@ -12,6 +12,7 @@ import {
   GetStationDevices, SaveStationDevices, GetStationStatus, StationSetRelay,
   GetRotatorHeading, RotatorGoTo, RotatorStop,
   GetUltrabeamStatus, SetUltrabeamDirection, UltrabeamRetract, MotorSetElement, MotorReadElements,
+  ListDenkoviDevices,
 } from '../../wailsjs/go/main/App';
 
 type RotatorProps = { centerLat?: number | null; centerLon?: number | null; bearing?: number | null };
@@ -20,8 +21,8 @@ type Device = { id: string; type: string; name: string; host: string; user?: str
 type Relay = { number: number; label: string; on: boolean };
 type DevStatus = { id: string; name: string; type: string; connected: boolean; error?: string; relays: Relay[] };
 
-const RELAY_COUNT: Record<string, number> = { webswitch: 5, kmtronic: 8 };
-const TYPE_LABEL: Record<string, string> = { webswitch: 'WebSwitch 1216H', kmtronic: 'KMTronic 8-relay' };
+const RELAY_COUNT: Record<string, number> = { webswitch: 5, kmtronic: 8, denkovi: 8 };
+const TYPE_LABEL: Record<string, string> = { webswitch: 'WebSwitch 1216H', kmtronic: 'KMTronic 8-relay', denkovi: 'Denkovi USB 8-relay' };
 
 function blankDevice(): Device {
   return { id: '', type: 'webswitch', name: '', host: '', user: '', pass: '', labels: Array(5).fill('') };
@@ -450,6 +451,21 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
     onChange({ ...device, type, labels });
   };
   const isKM = device.type === 'kmtronic';
+  const isDenkovi = device.type === 'denkovi';
+  // Detected FTDI serials for the Denkovi picker.
+  const [denkoviSerials, setDenkoviSerials] = useState<string[]>([]);
+  const [detecting, setDetecting] = useState(false);
+  const detectDenkovi = async () => {
+    setDetecting(true);
+    try {
+      const list = ((await ListDenkoviDevices()) ?? []) as string[];
+      setDenkoviSerials(list);
+      // Auto-fill when there's exactly one and nothing chosen yet.
+      if (list.length >= 1 && !device.host.trim()) onChange({ ...device, host: list[0] });
+    } catch { setDenkoviSerials([]); }
+    finally { setDetecting(false); }
+  };
+  useEffect(() => { if (isDenkovi) void detectDenkovi(); /* eslint-disable-next-line */ }, [isDenkovi]);
   return (
     <div ref={ref} className="mt-4 max-w-4xl rounded-xl border border-primary/40 bg-card p-4 space-y-3">
       <div className="text-sm font-semibold">{device.id ? t('station.editDevice') : t('station.addDevice')}</div>
@@ -461,6 +477,7 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
             <SelectContent>
               <SelectItem value="webswitch">WebSwitch 1216H (5 relays)</SelectItem>
               <SelectItem value="kmtronic">KMTronic 8-relay (LAN)</SelectItem>
+              <SelectItem value="denkovi">Denkovi USB 8-relay (FT245)</SelectItem>
             </SelectContent>
           </Select>
         </div>
@@ -469,6 +486,24 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
           <Input value={device.name} placeholder={TYPE_LABEL[device.type]} onChange={(e) => onChange({ ...device, name: e.target.value })} />
         </div>
       </div>
+      {isDenkovi ? (
+        <div className="space-y-1 max-w-md">
+          <Label>{t('station.ftdiSerial')}</Label>
+          <div className="flex items-center gap-2">
+            <Input className="font-mono flex-1" value={device.host} placeholder="DAE0006K"
+              list="denkovi-serials"
+              onChange={(e) => onChange({ ...device, host: e.target.value })} />
+            <datalist id="denkovi-serials">
+              {denkoviSerials.map((s) => <option key={s} value={s} />)}
+            </datalist>
+            <Button size="sm" variant="outline" onClick={detectDenkovi} disabled={detecting}>
+              {detecting ? <Loader2 className="size-3.5 mr-1 animate-spin" /> : <RefreshCw className="size-3.5 mr-1" />}
+              {t('station.detect')}
+            </Button>
+          </div>
+          <p className="text-[10px] text-muted-foreground">{t('station.ftdiHint')}</p>
+        </div>
+      ) : (
       <div className={cn('grid gap-3', isKM ? 'grid-cols-3' : 'grid-cols-1')}>
         <div className={cn('space-y-1', isKM ? '' : 'max-w-xs')}>
           <Label>{t('station.host')}</Label>
@@ -487,6 +522,7 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
           </>
         )}
       </div>
+      )}
       <div className="space-y-1">
         <Label>{t('station.labels')}</Label>
         <div className="grid grid-cols-4 gap-2">