Correct what the ETL, the code and the textures README said of their own sources and figures

- The IAU day check said it compared W with the period Horizons states. That holds for the eight
  planets and Phoebe only. Pluto's and Ceres's periods are the IAU's own rate restated (8.5e-12 and
  3.3e-10: Horizons' Pluto period is 360 over its W, and the SBDB notes it derived Ceres's from the
  report's 952.1532 degrees a day), and the 22 locked moons' is their orbit's, from JPL's table, not
  from their Horizons pages ("Synchronous" on eighteen, nothing on Titan's or Proteus's), and now
  their W's own rate. The comment, the log line and the error message say which is which; the log
  shows 0.0e+0 for the twenty locked moons turned at their orbit's rate, 1.1e-8 and 3.1e-7 for the
  Moon and Phobos. BodyRecord.rotationPeriodHours says that where a source states no period, or
  one a later measurement overturns, it is the one the ETL spec carries (Nereid's, Eris's), where
  the previous commit had Eris among the bodies whose source states none.
- Phoebe's spec justified its period by a note in the satellite table, which is about another
  source (Jacobson 2000, Jupiter's outer moons) and says the table carries corrected values. The
  row's n is right as the table defines it, the rate of the mean longitude: n less twice the node's
  rate is 0.6541855 degrees a day, against 360 / 550.30391 = 0.6541840. What made Phoebe drift is
  that the propagator reads a retrograde moon's n as its sidereal rate, as Triton's row gives it.
  The comment now says so; the period, 550.30391 days, is kept.
- body-orientation.ts and its spec said the IAU's W for Earth, "taken at UT", left its face 2.3 and
  4.5 degrees off Horizons at AD 1000 and AD 1. The old code took it at UT + 69.184 s; those are
  that figure's, and at UT itself they are 2.0 and 4.2, as three reviewers measured through the
  code (4.25, 4.25 and 4.28 at AD 1).
- The renderer said the 28 maps entering the Sun's system are about 20 megapixels of JPEG. Read
  from their frame headers: 37.75, nine at 2048 by 1024 with the Sun's, Jupiter's at 3840 by 1920
  and eighteen smaller.
- The textures README gave Titan 0.02 per cent unmapped, counting only the source's zeros. Its
  largest gap is a flat grey of the source's own (147 and 148, its two commonest values), which
  NASA's caption for PIA19658 names as the gap in coverage: measured on titan.jpg, one region of
  1.09 per cent of the pixels, 0.87 of the sphere, at 48-68 N and 37 W to 25 E. The row says 1.1 per
  cent and where, and step 1 says how it is counted; commit 302fa96's "the rest under 0.2%" is
  therefore not true of Titan.

No behaviour changes but the ETL's log and error wording; the solar ETL passes with the new text.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tools/etl/fetchSolarSystem.ts

@@ -137,11 +137,15 @@ const BODY_SPECS: BodySpec[] = [
   // Hyperion's eccentricity is 0.105 in JPL's current table (ssd.jpl.nasa.gov/sats/elem, SAT441).
   { id: 'hyperion', name: 'Hyperion', kind: 'moon', horizonsCommand: '607', center: '500@699', parentBodyId: 'saturn', spinsFreely: true, measuredEccentricity: 0.105, trackStepDays: 1 },
   { id: 'iapetus', name: 'Iapetus', kind: 'moon', horizonsCommand: '608', center: '500@699', parentBodyId: 'saturn', poleFollowsOrbit: true },
-  // Phoebe's row gives a mean motion of 0.6569114 degrees a day, a 548.02-day year, where its
-  // Horizons page and JPL's current table (SAT441) give 550.30: the table's own note warns that
-  // its source misstated the mean motions of retrograde moons. On the row's figure Phoebe was
-  // 25 degrees from Horizons by 2025 and 100 by 2075; on the current period, within 2.6 from 1950
-  // to 2100 (2.58 in 1969).
+  // Phoebe's row gives n = 0.6569114 degrees a day as the table defines it, the rate of its mean
+  // longitude, node plus periapsis plus mean anomaly, and its P, 548.02 days, is 360 over that. Its
+  // sidereal period is 550.30 (its Horizons page and JPL's current table, SAT441): n less twice its
+  // node's rate, 0.6541855, against 360 / 550.30391 = 0.6541840. Triton's row gives its sidereal
+  // rate as n instead, and the propagator reads a retrograde moon's n as that (see
+  // `meanElementsAt`): on the row's n Phoebe ran twice its node's rate too fast, 25 degrees from
+  // Horizons by 2025 and 100 by 2075. On the sidereal period it is within 2.6 from 1950 to 2100
+  // (2.58 in 1969). The table's note on misstated retrograde mean motions is about another source,
+  // Jacobson 2000 on Jupiter's outer moons, and says the table carries the corrected values.
   { id: 'phoebe', name: 'Phoebe', kind: 'moon', horizonsCommand: '609', center: '500@699', parentBodyId: 'saturn', spinsFreely: true, periodDays: 550.30391 },
   { id: 'miranda', name: 'Miranda', horizonsCommand: '705', ...URANUS_MOON },
   { id: 'ariel', name: 'Ariel', horizonsCommand: '701', ...URANUS_MOON },