feat(audio): transmit audio for WSJT-X through a network Icom

An IC-705, IC-7610 or IC-7760 on Ethernet has no sound card on this PC:
its receive audio arrives on UDP 50003 and its transmit audio has to go
back the same way. OpsLog already did both — the monitor plays the
stream, the voice keyer and the talk button send into it.

WSJT-X could not. It drives the rig through the CAT OpsLog shares, so it
tunes and keys perfectly well, and then has nowhere to put its audio: it
needs a Windows endpoint and the radio is not one. A virtual cable
bridges that, which is what wfview asks of its users too — nothing short
of a signed kernel driver can present a sound card.

So: a "WSJT-X transmit audio" device in Settings ▸ Audio, shown only
when To Radio is the radio itself, since a rig with a USB codec needs
none of this and WSJT-X talks to that codec directly.

Almost no new machinery. StartTXAudioNetwork already pipes a chosen
capture device into the rig — it was written for the talk button — and
the missing piece was only WHEN. That is catShareRig.SetPTT: WSJT-X keys
through us, so we know. Audio starts after the carrier and stops before
it, because the other order transmits what is still buffered after the
program thinks the over is finished.

Armed by PTT rather than left running: a permanent stream would put
whatever the cable carries — desktop notifications, another program that
grabbed the same cable — on the air the moment anything else keyed the
rig. And stopped only if WE started it, since the talk button and the
voice keyer share the same route and a digital over ending must not cut
off a message being played by hand.

Receive needs no code: point Listening at a second cable and WSJT-X's
input at its other side. The hint in Settings says so.

frontend/src/lib/i18n.tsx

@@ -577,7 +577,9 @@ const en: Dict = {
   'clg2.allFiltered': '{n} spots received, none shown — your filters are hiding them all.', 'clg2.activeFilters': 'Active:', 'clg2.clearAllFilters': 'Clear every filter', 'clg2.fBandLock': 'band locked to the rig', 'clg2.fBands': 'bands {list}', 'clg2.fModeLock': 'mode locked to the rig', 'clg2.fModes': 'modes {list}', 'clg2.fStatus': 'status chips', 'clg2.fHideWorked': 'hide worked', 'clg2.fLotwOnly': 'LoTW users only', 'clg2.fSpotterCont': 'spotter continent', 'clg2.fSource': 'one source node', 'clg2.fSearch': 'search “{q}”',
   'clg2.c.time': 'Time', 'clg2.c.call': 'Call', 'clg2.c.status': 'Status', 'clg2.c.pota': 'POTA', 'clg2.c.sota': 'SOTA', 'clg2.c.freq': 'Freq', 'clg2.c.band': 'Band', 'clg2.c.mode': 'Mode', 'clg2.c.pfx': 'Pfx', 'clg2.c.cqz': 'CQ Zone', 'clg2.h.cqz': 'CQZ', 'clg2.c.ituz': 'ITU Zone', 'clg2.h.ituz': 'ITU', 'clg2.c.distance_km': 'Distance (km)', 'clg2.h.distance_km': 'Dist km', 'clg2.c.sp_deg': 'Short path (°)', 'clg2.h.sp_deg': 'SP°', 'clg2.c.lp_deg': 'Long path (°)', 'clg2.h.lp_deg': 'LP°', 'clg2.c.country': 'Country', 'clg2.c.continent': 'Continent', 'clg2.h.continent': 'Cont', 'clg2.c.spotter': 'Spotter', 'clg2.c.source': 'Source', 'clg2.c.locator': 'Spotter locator', 'clg2.h.locator': 'Spotter loc', 'clg2.c.county': 'US County', 'clg2.tipNewCounty': 'NEW COUNTY — never worked', 'clg2.tipNewPfx': 'NEW PREFIX — this WPX prefix has never been worked', 'clg2.c.comment': 'Comment', 'clg2.c.received_at': 'Received at', 'clg2.h.received_at': 'Received UTC', 'clg2.c.raw': 'Raw', 'clg2.newDxcc': 'NEW DXCC', 'clg2.newBandMode': 'NEW B+M', 'clg2.newBand': 'NEW BAND', 'clg2.newMode': 'NEW MODE', 'clg2.newSlot': 'NEW SLOT', 'clg2.newCall': 'NEW CALL', 'clg2.wkdCall': 'WKD CALL', 'clg2.newCounty': 'NEW CTY', 'clg2.newGridUnconf': 'GRID?', 'clg2.newState': 'New State', 'clg2.newGrid': 'NEW GRID', 'clg2.c.grid': 'Grid', 'clg2.tipNewGrid': 'NEW GRID — this square has never been worked (grid heard in a CQ on the UDP link)', 'clg2.newPfx': "NEW PFX", 'clg2.newPota': 'NEW POTA', 'clg2.tipNewDxcc': 'NEW DXCC: {country}', 'clg2.tipWorkedCall': 'Already worked this call', 'clg2.tipNewBandMode': 'NEW BAND AND NEW MODE for this entity — neither has been worked with it', 'clg2.tipNewBand': 'NEW BAND for this entity', 'clg2.tipNewSlotBand': 'NEW SLOT (mode not yet worked on this band)', 'clg2.tipNewMode': 'NEW MODE (this mode never worked on this entity)', 'clg2.tipNewSlot': 'NEW SLOT (this band+mode not yet worked)', 'clg2.tipNewCall': 'NEW CALL — this callsign has never been worked on this band and mode (the entity has)', 'clg2.tipPota': 'POTA — {name}', 'clg2.grpSpot': 'Spot', 'clg2.grpGeo': 'Geo', 'clg2.clearFiltersTitle': 'Clear all column filters', 'clg2.clearFilters': 'Clear filters', 'clg2.newSpots': '{n} new spots — click to resume', 'clg2.columns': 'Columns', 'clg2.pickerTitle': 'Cluster columns', 'clg2.pickerDesc': 'Pick the columns you want visible in the Cluster table.', 'clg2.allGroups': 'All groups:', 'clg2.all': 'all', 'clg2.none': 'none', 'clg2.resetDefaults': 'Reset to defaults', 'clg2.done': 'Done',
   // Audio devices & voice keyer (Preferences → Audio devices).
-  'aud.refreshDevices': 'Refresh devices', 'aud.fromRadio': 'From Radio (RX in)', 'aud.toRadio': 'To Radio (TX out)', 'aud.recMic': 'Recording mic', 'aud.listening': 'Listening (preview)',
+  'aud.refreshDevices': 'Refresh devices',
+  'aud.digiInput': 'WSJT-X transmit audio', 'aud.phDigiInput': 'The virtual cable WSJT-X plays into',
+  'aud.digiInputHint': "Your radio has no sound card on this PC, so a digital program cannot reach it. Install a virtual audio cable, set WSJT-X's output to it, and choose the same cable's recording side here — OpsLog streams it to the radio while WSJT-X holds PTT through the shared CAT. For receive, point WSJT-X's input at a second cable and set Listening to it.", 'aud.fromRadio': 'From Radio (RX in)', 'aud.toRadio': 'To Radio (TX out)', 'aud.recMic': 'Recording mic', 'aud.listening': 'Listening (preview)',
   'aud.phFromRadio': 'Rig audio output → soundcard input', 'aud.phToRadio': 'Soundcard output → rig mic/data in', 'aud.phRecMic': 'Your microphone (record voice-keyer messages)', 'aud.phListening': 'Local speakers for preview',
   'aud.noneDefault': '— none / system default —', 'aud.defaultTag': '(default)',
   'aud.fromRadioShort': 'From Radio', 'aud.toRadioShort': 'To Radio', 'aud.explainFrom': '= what you receive (used by the QSO recorder).', 'aud.explainTo': '= where voice-keyer messages are transmitted.',
@@ -1205,7 +1207,9 @@ const fr: Dict = {
   'clg2.allFiltered': '{n} spots reçus, aucun affiché — vos filtres les masquent tous.', 'clg2.activeFilters': 'Actifs :', 'clg2.clearAllFilters': 'Effacer tous les filtres', 'clg2.fBandLock': 'bande verrouillée sur la radio', 'clg2.fBands': 'bandes {list}', 'clg2.fModeLock': 'mode verrouillé sur la radio', 'clg2.fModes': 'modes {list}', 'clg2.fStatus': 'pastilles de statut', 'clg2.fHideWorked': 'masquer les contactés', 'clg2.fLotwOnly': 'utilisateurs LoTW uniquement', 'clg2.fSpotterCont': 'continent du spotteur', 'clg2.fSource': 'un seul nœud source', 'clg2.fSearch': 'recherche « {q} »',
   'clg2.c.time': 'Heure', 'clg2.c.call': 'Indicatif', 'clg2.c.status': 'Statut', 'clg2.c.pota': 'POTA', 'clg2.c.sota': 'SOTA', 'clg2.c.freq': 'Fréq', 'clg2.c.band': 'Bande', 'clg2.c.mode': 'Mode', 'clg2.c.pfx': 'Préf.', 'clg2.c.cqz': 'Zone CQ', 'clg2.h.cqz': 'CQZ', 'clg2.c.ituz': 'Zone ITU', 'clg2.h.ituz': 'ITU', 'clg2.c.distance_km': 'Distance (km)', 'clg2.h.distance_km': 'Dist km', 'clg2.c.sp_deg': 'Chemin court (°)', 'clg2.h.sp_deg': 'CC°', 'clg2.c.lp_deg': 'Chemin long (°)', 'clg2.h.lp_deg': 'CL°', 'clg2.c.country': 'Pays', 'clg2.c.continent': 'Continent', 'clg2.h.continent': 'Cont', 'clg2.c.spotter': 'Spotter', 'clg2.c.source': 'Source', 'clg2.c.locator': 'Locator du spotter', 'clg2.h.locator': 'Loc spotter', 'clg2.c.county': 'Comté US', 'clg2.tipNewCounty': 'NOUVEAU COMTÉ — jamais contacté', 'clg2.tipNewPfx': "NOUVEAU PRÉFIXE — ce préfixe WPX n'a jamais été contacté", 'clg2.c.comment': 'Commentaire', 'clg2.c.received_at': 'Reçu le', 'clg2.h.received_at': 'Reçu UTC', 'clg2.c.raw': 'Brut', 'clg2.newDxcc': 'NOUV DXCC', 'clg2.newBandMode': 'NOUV B+M', 'clg2.newBand': 'NOUV BANDE', 'clg2.newMode': 'NOUV MODE', 'clg2.newSlot': 'NOUV SLOT', 'clg2.newCall': 'CALL NEUF', 'clg2.wkdCall': 'DÉJÀ QSO', 'clg2.newCounty': 'NOUV CTY', 'clg2.newGridUnconf': 'GRID?', 'clg2.newState': 'Nouvel État', 'clg2.newGrid': 'NOUV GRID', 'clg2.c.grid': 'Grid', 'clg2.tipNewGrid': 'NOUVEAU GRID — ce carré n a jamais été contacté (grid entendu dans un CQ sur le lien UDP)', 'clg2.newPfx': "NOUVEAU PFX", 'clg2.newPota': 'NOUV POTA', 'clg2.tipNewDxcc': 'NOUVEAU DXCC : {country}', 'clg2.tipWorkedCall': 'Indicatif déjà contacté', 'clg2.tipNewBandMode': 'NOUVELLE BANDE ET NOUVEAU MODE pour cette entité — aucun des deux n’a été fait avec elle', 'clg2.tipNewBand': 'NOUVELLE BANDE pour cette entité', 'clg2.tipNewSlotBand': 'NOUVEAU SLOT (mode pas encore contacté sur cette bande)', 'clg2.tipNewMode': 'NOUVEAU MODE (ce mode jamais contacté sur cette entité)', 'clg2.tipNewSlot': 'NOUVEAU SLOT (cette bande+mode pas encore contactée)', 'clg2.tipNewCall': "CALL NEUF — cet indicatif n a jamais été contacté sur cette bande et ce mode (l entité, si)", 'clg2.tipPota': 'POTA — {name}', 'clg2.grpSpot': 'Spot', 'clg2.grpGeo': 'Géo', 'clg2.clearFiltersTitle': 'Effacer tous les filtres de colonne', 'clg2.clearFilters': 'Effacer les filtres', 'clg2.newSpots': '{n} nouveaux spots — cliquer pour reprendre', 'clg2.columns': 'Colonnes', 'clg2.pickerTitle': 'Colonnes du cluster', 'clg2.pickerDesc': 'Choisissez les colonnes à afficher dans le tableau du cluster.', 'clg2.allGroups': 'Tous les groupes :', 'clg2.all': 'tout', 'clg2.none': 'aucun', 'clg2.resetDefaults': 'Réinitialiser', 'clg2.done': 'Terminé',
   // Périphériques audio et manipulateur vocal (Préférences → Périphériques audio).
-  'aud.refreshDevices': 'Actualiser les périphériques', 'aud.fromRadio': 'Depuis la radio (entrée RX)', 'aud.toRadio': 'Vers la radio (sortie TX)', 'aud.recMic': "Micro d'enregistrement", 'aud.listening': 'Écoute (pré-écoute)',
+  'aud.refreshDevices': 'Actualiser les périphériques',
+  'aud.digiInput': 'Audio d’émission WSJT-X', 'aud.phDigiInput': 'Le câble virtuel dans lequel WSJT-X émet',
+  'aud.digiInputHint': "Votre radio n'a pas de carte son sur ce PC, un logiciel numérique ne peut donc pas l'atteindre. Installez un câble audio virtuel, réglez la sortie de WSJT-X dessus, et choisissez ici le côté enregistrement du même câble — OpsLog le diffuse vers la radio pendant que WSJT-X tient le PTT via le CAT partagé. Pour la réception, pointez l'entrée de WSJT-X sur un second câble et réglez « Écoute » dessus.", 'aud.fromRadio': 'Depuis la radio (entrée RX)', 'aud.toRadio': 'Vers la radio (sortie TX)', 'aud.recMic': "Micro d'enregistrement", 'aud.listening': 'Écoute (pré-écoute)',
   'aud.phFromRadio': 'Sortie audio du poste → entrée carte son', 'aud.phToRadio': 'Sortie carte son → entrée micro/data du poste', 'aud.phRecMic': 'Votre microphone (enregistrer les messages vocaux)', 'aud.phListening': 'Haut-parleurs locaux pour la pré-écoute',
   'aud.noneDefault': '— aucun / défaut système —', 'aud.defaultTag': '(défaut)',
   'aud.fromRadioShort': 'Depuis la radio', 'aud.toRadioShort': 'Vers la radio', 'aud.explainFrom': "= ce que vous recevez (utilisé par l'enregistreur de QSO).", 'aud.explainTo': '= où sont émis les messages du manipulateur vocal.',