feat(ftmap): a layer for who hears me

The map drew one direction of every path on it: what this receiver
decoded. The reverse — which stations are reporting our own
transmissions — is the half an operator cannot see from their own
radio, and on FT8 it is the half that decides whether calling is worth
the cycle.

It is the narrowest slice of the PSK Reporter feed there is. The v2
topic is

	pskr/filter/v2/<band>/<mode>/<tx call>/<rx call>/…

so putting the operator's callsign in the TRANSMIT level makes the
broker send nothing else. For scale, from internal/pskr's own measured
numbers: four bands unfiltered is 83 messages a second, filtered on the
receiver's square 0.2 to 1.2 a second — one callsign in the transmit
level is a handful per FT8 cycle however open the band is. Both grids
are in the payload, so the arc is arithmetic and there is no lookup.

internal/pskrme, with its own connection, for the same reason
internal/pskrtgt has its own: the three want slices of the feed that
cannot be filtered out of one another. It also means this keeps working
with the band-opening watch off — hanging it off that feed's lifecycle
would have made it fail silently for anyone not chasing openings.

Nothing is persisted. One entry per STATION inside a fifteen-minute
window, carrying its freshest report: PSK Reporter's uploaders batch,
many every five minutes, so a tighter window would show a fraction of
who actually heard the last few calls. Stop clears the window, or
switching the layer back on would redraw who heard us before it was on.

On the map the layer is dashed and single-coloured. Solid is what we
decoded, dashed is somebody decoding us; colour alone could not carry
that distinction next to fourteen band colours. The receivers are rings
rather than filled dots for the same reason. Per profile, since the
callsign IS the subscription — a switch resubscribes rather than going
on reporting who hears the previous station.

frontend/src/lib/i18n.tsx

@@ -199,7 +199,7 @@ const en: Dict = {
   'wlc.title': 'Contest', 'wlc.pattern': 'Auto-add on', 'wlc.patternPh': 'WWA', 'wlc.patternHint': 'any spotted callsign CONTAINING this joins the watchlist as a contest entry (TM29WWA, HB9WWA, F4WWA/P)',
   'wlc.calls': 'And these callsigns, one per line', 'wlc.callsPh': 'R7W  DL0ABC', 'wlc.callsHint': 'For the entries a pattern cannot catch: a station taking part under a callsign that says nothing about the event. Named here, it joins the contest watchlist the moment it is spotted. Commas and spaces work too.',
   // FTx decodes panel (Tools -> FT decodes)
-  'ftmap.tab': 'FT Map', 'ftmap.noGrid': 'Set your station grid in Preferences to place the map.', 'ftmap.colour': 'One colour for every decode, whatever the band', 'ftmap.colourPerBand': 'Back to the colour per band', 'dec.tab': 'FT decodes', 'dec.title': 'Decodes', 'dec.bandDrift': '{app} says {dec}, the rig is on {rig}', 'dec.bandDriftApp': 'the decoder', 'dec.bandDriftTip': 'The decoding application is announcing a band the radio is not on — it has most likely lost its CAT link and is repeating the last frequency it knew. Every decode below carries that band, so the NEW / NEW BAND verdicts are judged against it.', 'dec.cqOnly': 'CQ only', 'dec.sortTip': 'Sort this slot by this column. Click again to reverse it, once more for the order the decoder heard them in.',
+  'ftmap.tab': 'FT Map', 'ftmap.noGrid': 'Set your station grid in Preferences to place the map.', 'ftmap.colour': 'One colour for every decode, whatever the band', 'ftmap.colourPerBand': 'Back to the colour per band', 'ftmap.hearMe': 'Who hears me', 'ftmap.hearMeTip': 'Draw the stations reporting your own transmissions to PSK Reporter, dashed, alongside what you decode. Watches one topic — your callsign — so it costs almost nothing.', 'ftmap.hearMeLegend': 'reporting you ({n})', 'dec.tab': 'FT decodes', 'dec.title': 'Decodes', 'dec.bandDrift': '{app} says {dec}, the rig is on {rig}', 'dec.bandDriftApp': 'the decoder', 'dec.bandDriftTip': 'The decoding application is announcing a band the radio is not on — it has most likely lost its CAT link and is repeating the last frequency it knew. Every decode below carries that band, so the NEW / NEW BAND verdicts are judged against it.', 'dec.cqOnly': 'CQ only', 'dec.sortTip': 'Sort this slot by this column. Click again to reverse it, once more for the order the decoder heard them in.',
   'dec.allBands': 'All bands', 'dec.allModes': 'All modes', 'toast.qsoLogged': 'QSO logged', 'dec.contsHint': 'Continents: click to keep one or several', 'dec.allConts': 'All continents',
   'dec.minSnrTitle': 'Hide anything weaker than this SNR', 'dec.searchPh': 'Call, grid or message',
   'dec.clearFilters': 'Clear', 'dec.live': 'live', 'dec.tx': 'TX',
@@ -840,7 +840,7 @@ const fr: Dict = {
   'wlc.title': 'Contest', 'wlc.pattern': 'Ajout auto sur', 'wlc.patternPh': 'WWA', 'wlc.patternHint': 'tout indicatif spotté CONTENANT ceci rejoint la watchlist comme entrée contest (TM29WWA, HB9WWA, F4WWA/P)',
   'wlc.calls': 'Et ces indicatifs, un par ligne', 'wlc.callsPh': 'R7W  DL0ABC', 'wlc.callsHint': 'Pour les participants qu’aucun motif ne peut attraper : une station engagée sous un indicatif qui ne dit rien de l’événement. Nommée ici, elle rejoint la watchlist contest dès qu’elle est spottée. Les virgules et les espaces marchent aussi.',
   // Panneau des decodes FTx (Outils -> Decodes FT)
-  'ftmap.tab': 'FT Map', 'ftmap.noGrid': 'Renseigne ton locator dans les Préférences pour placer la carte.', 'ftmap.colour': 'Une seule couleur pour tous les décodages, quelle que soit la bande', 'ftmap.colourPerBand': 'Revenir à la couleur par bande', 'dec.tab': 'Decodes FT', 'dec.title': 'Decodes', 'dec.bandDrift': '{app} annonce {dec}, le poste est sur {rig}', 'dec.bandDriftApp': 'le décodeur', 'dec.bandDriftTip': 'Le logiciel de décodage annonce une bande sur laquelle la radio n’est pas — il a très probablement perdu sa liaison CAT et répète la dernière fréquence connue. Tous les décodages ci-dessous portent cette bande, et les verdicts NOUVEAU / NOUVELLE BANDE sont jugés dessus.', 'dec.cqOnly': 'CQ seulement', 'dec.sortTip': 'Trier ce créneau sur cette colonne. Un second clic inverse, un troisième rend l’ordre dans lequel le décodeur les a entendus.',
+  'ftmap.tab': 'FT Map', 'ftmap.noGrid': 'Renseigne ton locator dans les Préférences pour placer la carte.', 'ftmap.colour': 'Une seule couleur pour tous les décodages, quelle que soit la bande', 'ftmap.colourPerBand': 'Revenir à la couleur par bande', 'ftmap.hearMe': 'Qui m’entend', 'ftmap.hearMeTip': 'Trace en pointillés les stations qui rapportent vos émissions à PSK Reporter, à côté de ce que vous décodez. Un seul topic surveillé — votre indicatif — donc un coût quasi nul.', 'ftmap.hearMeLegend': 'vous rapportent ({n})', 'dec.tab': 'Decodes FT', 'dec.title': 'Decodes', 'dec.bandDrift': '{app} annonce {dec}, le poste est sur {rig}', 'dec.bandDriftApp': 'le décodeur', 'dec.bandDriftTip': 'Le logiciel de décodage annonce une bande sur laquelle la radio n’est pas — il a très probablement perdu sa liaison CAT et répète la dernière fréquence connue. Tous les décodages ci-dessous portent cette bande, et les verdicts NOUVEAU / NOUVELLE BANDE sont jugés dessus.', 'dec.cqOnly': 'CQ seulement', 'dec.sortTip': 'Trier ce créneau sur cette colonne. Un second clic inverse, un troisième rend l’ordre dans lequel le décodeur les a entendus.',
   'dec.allBands': 'Toutes bandes', 'dec.allModes': 'Tous modes', 'toast.qsoLogged': 'QSO enregistré', 'dec.contsHint': 'Continents : clique pour en garder un ou plusieurs', 'dec.allConts': 'Tous continents',
   'dec.minSnrTitle': 'Masquer tout ce qui est plus faible que ce rapport', 'dec.searchPh': 'Indicatif, locator ou message',
   'dec.clearFilters': 'Effacer', 'dec.live': 'en direct', 'dec.tx': 'TX',