feat(psu): switch a Modbus RTU bench supply from OpsLog

The manufacturer's document arrived, so this is no longer guesswork: 9600 8N1,
function codes 03 and 06 only, and a register map with the output on/off at
0x0001, the measurements at 0x0010…0x0013 and the set points at 0x0030/0x0031.

ONE REGISTER IS WRITTEN — 0x0001, the output. The map also exposes the voltage
and current set points and the three protection trip levels as writable, and
none of them belong to a logbook: a wrong value there is 30 V where a radio
expected 13.8, or a trip level lifted on a supply feeding an amplifier. They are
read and displayed instead, next to the measured values, which is also how an
operator sees at a glance that the supply is on and the radio is drawing nothing.

The wire layer is tested where it can be. CRC-16/MODBUS is pinned against its
published check value — the CRC of "123456789" is 0x4B37 — which fixes the
polynomial, the initial value, the reflection and the absence of a final xor all
at once; the rest of the protocol is checked frame by frame against the manual,
including the byte order of the CRC, an exception reply told apart from a broken
line, and a reply from another slave on the bus refused. The write echo must
match the value sent: it is the only confirmation the output really switched,
and accepting the frame without it is how a radio ends up dark behind a green
light.

Framing follows the manual's own rules: 3.5 character times of silence between
frames (4 ms at 9600), and a frame is over when the line falls quiet — Modbus
RTU has no terminator, and a serial read that times out returns (0, nil) here,
so the reader is built on a deadline and a quiet-time rather than on an error
that never comes.

Untested against hardware — nobody here has the supply.

frontend/src/components/SettingsModal.tsx

@@ -14,6 +14,7 @@ import {
   GetUltrabeamSettings, SaveUltrabeamSettings, TestUltrabeam,
   GetAntGeniusSettings, SaveAntGeniusSettings,
   GetTunerGeniusSettings, SaveTunerGeniusSettings,
+  GetPSUSettings, SavePSUSettings,
   GetAmplifiers, SaveAmplifiers, GetAmpStatuses, AmpOperate,
   GetWinkeyerSettings, SaveWinkeyerSettings, ListSerialPorts,
   GetAudioSettings, SaveAudioSettings, AudioApplyLevels, ListAudioInputDevices, ListAudioOutputDevices, PickAudioFolder, TestPTT,
@@ -203,6 +204,7 @@ type SectionId =
   | 'antenna'
   | 'antgenius'
   | 'tunergenius'
+  | 'psu'
   | 'pgxl'
   | 'flex'
   | 'relayauto'
@@ -251,6 +253,7 @@ function buildTree(flexAvailable: boolean, t: (k: string) => string): TreeNode[]
     { kind: 'item', label: t('sec.antgenius'),    id: 'antgenius',   vendor: 'o3a' },
     { kind: 'item', label: t('sec.tunergenius'),  id: 'tunergenius', vendor: 'o3a' },
     { kind: 'item', label: t('sec.pgxl'),         id: 'pgxl' },
+    { kind: 'item', label: t('sec.psu'),          id: 'psu' },
     ...(flexAvailable ? [{ kind: 'item', label: t('sec.flex'), id: 'flex' } as TreeNode] : []),
     { kind: 'item', label: t('sec.relayauto'),    id: 'relayauto' },
     { kind: 'item', label: t('sec.audio'),        id: 'audio' },
@@ -1278,6 +1281,7 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
   // Antenna Genius (4O3A) switch settings — TCP port is fixed at 9007.
   const [antgenius, setAntgenius] = useState<{ enabled: boolean; host: string; password: string }>({ enabled: false, host: '', password: '' });
   const [tunergenius, setTunergenius] = useState<{ enabled: boolean; host: string; password: string }>({ enabled: false, host: '', password: '' });
+  const [psuCfg, setPsuCfg] = useState<{ enabled: boolean; com_port: string; baud: number; address: number }>({ enabled: false, com_port: '', baud: 9600, address: 1 });
 
   // Amplifier list — operators can run SEVERAL amps (even two SPEs combined),
   // each with its own connection. Saved as a whole via SaveAmplifiers.
@@ -1681,6 +1685,7 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
         try { setUltrabeam(await GetUltrabeamSettings() as any); } catch {}
         try { setAntgenius(await GetAntGeniusSettings() as any); } catch {}
         try { setTunergenius(await GetTunerGeniusSettings() as any); } catch {}
+        try { setPsuCfg(await GetPSUSettings() as any); } catch {}
         try { setAmps(((await GetAmplifiers()) ?? []) as AmpUI[]); } catch {}
         setBackupCfg(b as any);
         setQslDefaults(qd as any);
@@ -1723,6 +1728,7 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
         try { setUltrabeam(await GetUltrabeamSettings() as any); } catch {}
         try { setAntgenius(await GetAntGeniusSettings() as any); } catch {}
         try { setTunergenius(await GetTunerGeniusSettings() as any); } catch {}
+        try { setPsuCfg(await GetPSUSettings() as any); } catch {}
         try { setAmps(((await GetAmplifiers()) ?? []) as AmpUI[]); } catch {}
         try { setBackupCfg(await GetBackupSettings() as any); } catch {}
         try { setQslDefaults(await GetQSLDefaults() as any); } catch {}
@@ -1916,6 +1922,7 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
       await SaveUltrabeamSettings(ultrabeam as any);
       await SaveAntGeniusSettings(antgenius as any);
       await SaveTunerGeniusSettings(tunergenius as any);
+      await SavePSUSettings(psuCfg as any);
       await SaveAmplifiers(amps as any);
       await SaveWinkeyerSettings(wk as any);
       await SaveAudioSettings(audioCfg as any);
@@ -3383,6 +3390,55 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
     );
   }
 
+  // Bench power supply over Modbus RTU. OpsLog reads everything and writes one
+  // register — the output on/off. The voltage and current SET points are shown
+  // because they are worth seeing, and are not editable here: they belong to the
+  // supply's front panel, and a logbook that can set them can set them wrong.
+  function PSUPanelSettings() {
+    const [ports, setPorts] = useState<string[]>([]);
+    useEffect(() => { ListSerialPorts().then((p) => setPorts((p ?? []) as string[])).catch(() => setPorts([])); }, []);
+    return (
+      <>
+        <SectionHeader title={t('psu.title')} hint={t('psu.hint')} />
+        <div className="space-y-4 max-w-xl">
+          <label className="flex items-center gap-2 text-sm cursor-pointer">
+            <Checkbox checked={psuCfg.enabled} onCheckedChange={(c) => setPsuCfg((s) => ({ ...s, enabled: !!c }))} />
+            {t('psu.enable')}
+          </label>
+          <div className="grid grid-cols-3 gap-3">
+            <div className="space-y-1">
+              <Label>{t('psu.port')}</Label>
+              <div className="flex items-center gap-2">
+                <Select value={psuCfg.com_port || '_'} onValueChange={(v) => setPsuCfg((s) => ({ ...s, com_port: v === '_' ? '' : v }))}>
+                  <SelectTrigger className="h-9 flex-1"><SelectValue placeholder="— COM —" /></SelectTrigger>
+                  <SelectContent>
+                    {ports.length === 0 && <SelectItem value="_" disabled>{t('station.noPorts')}</SelectItem>}
+                    {ports.map((p) => <SelectItem key={p} value={p}>{p}</SelectItem>)}
+                  </SelectContent>
+                </Select>
+                <Button size="sm" variant="outline" onClick={() => ListSerialPorts().then((p) => setPorts((p ?? []) as string[])).catch(() => {})}>
+                  ↻
+                </Button>
+              </div>
+            </div>
+            <div className="space-y-1">
+              <Label>{t('psu.baud')}</Label>
+              <Input className="font-mono" value={String(psuCfg.baud ?? 9600)}
+                onChange={(e) => setPsuCfg((s) => ({ ...s, baud: parseInt(e.target.value.replace(/[^0-9]/g, ''), 10) || 0 }))} />
+            </div>
+            <div className="space-y-1">
+              <Label>{t('psu.address')}</Label>
+              <Input className="font-mono" value={String(psuCfg.address ?? 1)}
+                onChange={(e) => setPsuCfg((s) => ({ ...s, address: parseInt(e.target.value.replace(/[^0-9]/g, ''), 10) || 0 }))} />
+            </div>
+          </div>
+          <p className="text-xs text-muted-foreground">{t('psu.wireHint')}</p>
+          <p className="text-xs text-warning">{t('psu.writeScope')}</p>
+        </div>
+      </>
+    );
+  }
+
   function PGXLPanelSettings() {
     // The stored `type` stays a flat value ("spe13", "acom700", "pgxl"); the UI
     // presents it as brand + model.
@@ -6349,6 +6405,7 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
     antenna:        UltrabeamPanel,
     antgenius:      AntGeniusPanelSettings,
     tunergenius:    TunerGeniusPanelSettings,
+    psu:            PSUPanelSettings,
     pgxl:           PGXLPanelSettings,
     flex:           () => <FlexBandPanel bands={lists.bands ?? []} />,
     audio:          AudioPanel,