fix(sat): the Doppler correction was 250 times too big, and backwards

Reported as "the Doppler moves the frequency enormously", and it did: a 2 m
downlink was being shifted two megahertz across a pass instead of three
kilohertz, in the wrong direction.

The propagator library reports a range rate that is not one. Measured against
the range it is meant to be the derivative of, on this station's own cached
elements:

    PO-101   library -1457.3 km/s    measured +6.227 km/s
    ISS      library +2036.8 km/s    measured -5.522 km/s

Wrong by a factor of some 250 and of the wrong sign, so the correction both
overshot and pushed the operator away from the station they could hear. Nothing
else was affected — the elevation and the passes come from the look angle, which
is right — which is why this survived: the satellite was in the correct place on
the map while the radio was told to go megahertz away from it.

So OpsLog computes it itself, as the difference between two ranges a second
apart. That cannot be wrong in either magnitude or sign: it differentiates the
very number the panel displays. Two extra propagations per call, which is
microseconds.

Two tests pin it, and both fail against the old behaviour: a range rate faster
than orbital velocity is a units mistake, and the Doppler on the two bands
satellites are worked on has a textbook size — about ±3.5 kHz on 2 m, ±10 kHz on
70 cm.

cmd/satdiag is the throwaway that found it, kept because the next report of this
shape ("the frequency moves oddly", "that pass is not real") is answered by the
same three numbers: which elements the satellite resolved to, the range rate
reported against the range rate measured, and the Doppler each transponder gets.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

changelog.json

@@ -1,4 +1,14 @@
 [
+  {
+    "version": "0.27.21",
+    "date": "",
+    "en": [
+      "The Doppler correction was wrong — by a factor of about 250, and in the wrong direction. The SGP4 library reports a range rate that is not one: the ISS closing at 5.5 km/s came back as +2036 km/s, which moved a 2 m downlink two megahertz instead of three kilohertz, and moved it the wrong way. OpsLog now measures the range rate from the range itself, which cannot disagree with physics. A 2 m downlink shifts about ±3.5 kHz across a pass and a 70 cm one about ±10 kHz, as they should."
+    ],
+    "fr": [
+      "La correction Doppler était fausse — d’un facteur d’environ 250, et dans le mauvais sens. La bibliothèque SGP4 renvoie une vitesse radiale qui n’en est pas une : l’ISS se rapprochant à 5,5 km/s était rapportée à +2036 km/s, ce qui déplaçait une descente 2 m de deux mégahertz au lieu de trois kilohertz, et dans la mauvaise direction. OpsLog mesure désormais cette vitesse à partir de la distance elle-même, ce qui ne peut pas contredire la physique. Une descente 2 m se décale d’environ ±3,5 kHz sur un passage et une 70 cm d’environ ±10 kHz, comme il se doit."
+    ]
+  },
   {
     "version": "0.27.20",
     "date": "",