feat(sat): Doppler tracking on the radio

The hard part of satellite tuning is not the arithmetic, it is deciding
who owns the dial. A tracker that forces both frequencies fights the
operator every time they turn the knob to follow a station across a
linear transponder; one that never touches the receiver leaves them
chasing a signal that slides nine kilohertz across a 70 cm pass.

So the operator owns the receiver and the tracker follows them. Every
second it asks the radio where the receiver actually is. Where it put it,
nothing has changed. Further than a dial-turn's tolerance, and the
operator has chosen a station: what they landed on is converted back into
a nominal frequency, and the transmitter is derived from that. Which is
the division of labour on a linear bird — the operator listens, the radio
does the sums.

Three ways to reach the radio, because a satellite pair is a shape of
operating rather than a manufacturer's feature. An IC-9700 or IC-9100 is
asked for its OWN satellite mode: it pairs main and sub, gives full
duplex, and keeps the dials linked the way its designers meant, which is
always better than an imitation built out of split. A Flex gets two
slices, A the downlink and B the uplink, created when missing, because
"slice B does not exist" is not something to make an operator fix at the
start of a ten-minute pass. Everything else gets the downlink, and is
told so — half the job announced beats half the job hidden.

What goes in the log is the NOMINAL pair. Two stations working each other
through a transponder read different numbers off their dials at the same
instant; the only figure they can both agree on is the transponder's own.
FREQ is the uplink and FREQ_RX the downlink — the one place a satellite
QSO differs from every other kind, and the reason FREQ alone cannot
describe one.

frontend/src/lib/i18n.tsx

@@ -582,6 +582,11 @@ const en: Dict = {
   'sat.noElements': 'no elements', 'sat.inverting': 'inverting', 'sat.geo': 'geostationary', 'sat.favTip': 'Track this satellite by default',
   'sat.paste': 'Paste…', 'sat.pasteTip': 'Paste elements for a satellite no feed carries yet. They are kept in their own file and survive every refresh.',
   'sat.pastePrompt': 'Paste the elements (name, then the two lines):', 'sat.pasteNone': 'Nothing usable in that text.',
+  'sat.track': 'Track', 'sat.tracking': 'Tracking',
+  'sat.trackTip': 'Put the radio on this satellite and keep it there: the downlink and the uplink both corrected for Doppler, once a second. Tune the receiver freely — the transmitter follows where you land.',
+  'sat.trackingFull': 'Tracking both ends of the pass. Tune the receiver freely; the transmitter follows.',
+  'sat.trackingDown': 'Tracking the downlink only — this radio has one receiver.',
+  'sat.downlinkOnly': 'downlink only', 'sat.nominal': 'nominal',
 };
 
 const fr: Dict = {
@@ -1127,6 +1132,11 @@ const fr: Dict = {
   'sat.noElements': 'sans éléments', 'sat.inverting': 'inverseur', 'sat.geo': 'géostationnaire', 'sat.favTip': 'Suivre ce satellite par défaut',
   'sat.paste': 'Coller…', 'sat.pasteTip': 'Collez les éléments d’un satellite qu’aucun flux ne diffuse encore. Ils sont conservés dans leur propre fichier et survivent à chaque mise à jour.',
   'sat.pastePrompt': 'Collez les éléments (nom, puis les deux lignes) :', 'sat.pasteNone': 'Rien d’utilisable dans ce texte.',
+  'sat.track': 'Suivre', 'sat.tracking': 'Suivi',
+  'sat.trackTip': 'Met la radio sur ce satellite et l’y garde : descente et montée corrigées du Doppler, chaque seconde. Accordez le récepteur librement — l’émetteur suit là où vous vous posez.',
+  'sat.trackingFull': 'Les deux bouts du passage sont suivis. Accordez le récepteur librement, l’émetteur suit.',
+  'sat.trackingDown': 'Seule la descente est suivie — cette radio n’a qu’un récepteur.',
+  'sat.downlinkOnly': 'descente seule', 'sat.nominal': 'nominal',
 };
 
 const dicts: Record<Lang, Dict> = { en, fr };