Give an archive star's distance error as the error on the distance it is, not as a parallax range

formatDistance printed any error of a fifth or more as the range a parallax's error makes,
d/(1+e) to d/(1−e). A star the ETL places from the Exoplanet Archive carries the mean of sy_disterr1
and 2 instead, which the archive defines as one-sided errors on sy_dist in parsecs, and many of
those distances come from a lensing model with no parallax behind them. 129 of the 3 195 archive
stars with an error were printed as ranges the archive does not give: KMT-2016-BLG-1836L as 5.8 to
9.2 kpc, where the archive publishes 7 100 +800 −2 400 pc, and AT2021ueyL as 664 pc to 2.4 kpc
against 1 040 +740 −440.

The card now tells formatDistance when the error is on the distance (source exoplanet-archive), and
it keeps the ± at any size. Measured on the shipped catalogue: KMT-2016-BLG-1836L reads 7.1 ± 1.6 kpc,
AT2021ueyL 1.0 ± 0.6 kpc, EPIC 201170410 134 ± 43 pc, KMT-2016-BLG-0212L 6.3 ± 1.3 kpc. The ETL keeps
only the mean, so a lopsided interval such as KMT-2016-BLG-1836L's is shown symmetric; carrying both
errors would take a second column in stars-meta.bin. The doc comments on formatDistance and on
distanceError no longer say an archive distance is an inverted parallax.

Controls, each failing its named test: the error on the distance read as a parallax's (2 of 790
failed), and the card not saying it is on the distance (1 of 790).

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

src/app/shared/models/star.model.ts

@@ -35,7 +35,9 @@ export interface StarRecord {
   colorSystem?: 'B-V' | 'BP-RP';
   /**
    * Relative uncertainty of the distance, σd/d: the relative error of the parallax it was
-   * inverted from, which to first order is the same. Absent where none was published.
+   * inverted from, which to first order is the same — or, for a star the Exoplanet Archive places,
+   * the mean of the two one-sided errors it gives on the distance itself, which is often no
+   * parallax's. Absent where none was published.
    */
   distanceError?: number;
   /** Whether the distance is Gaia DR3's parallax, whichever catalogue describes the star. */