feat: the offline FCC database answers during entry, not only at save

ULS was wired into AddQSO alone, so an operator who downloaded it and has no
QRZ.com/HamQTH account saw nothing while typing a US call: cty.dat gives the
country, the zones, and a 4-character grid that is the ENTITY centroid — a
thousand kilometres from the station. The county and the real square were stamped
after logging, too late to point an antenna with.

The enrichment runs last in the lookup wrapper and only fills blanks, so a
provider always wins. ULS carries no name and no address, so it completes a QRZ
record and can never replace one.

The grid needed a rule of its own. refineGrid keeps what is there unless the new
value extends it — correct for a QRZ square, wrong against an entity centroid,
which is simply a different square. A per-callsign FCC square therefore beats any
4-character grid, while a 6-character one already present is left untouched.
Lat/lon are recomputed only when we actually moved the grid.

Portable calls are skipped: W1AW/4 is not what the FCC licensed.

changelog.json

@@ -3,9 +3,11 @@
     "version": "0.21.9",
     "date": "2026-07-28",
     "en": [
+      "The offline FCC (ULS) database now answers while you type a US callsign, filling state, county and a 6-character grid. It was only applied when the QSO was saved, so without a QRZ.com or HamQTH account you saw nothing but the country and a coarse grid. Online lookups still win — ULS only fills what is blank.",
       "CQ and ITU zones you correct by hand in your profile stay corrected. They are derived from cty.dat, which gives the zones of the whole entity — in a country spanning several, the automatic value is wrong and it came back at every restart. They now only fill in when empty, and recompute when the callsign or grid changes."
     ],
     "fr": [
+      "La base FCC (ULS) hors ligne répond désormais pendant la saisie d'un indicatif américain, en remplissant l'état, le comté et un locator 6 caractères. Elle n'était appliquée qu'à l'enregistrement du QSO : sans compte QRZ.com ou HamQTH, vous ne voyiez que le pays et un locator approximatif. Les recherches en ligne restent prioritaires — l'ULS ne comble que ce qui est vide.",
       "Les zones CQ et ITU corrigées à la main dans votre profil restent corrigées. Elles proviennent de cty.dat, qui donne les zones de l'entité entière — dans un pays qui en couvre plusieurs, la valeur automatique est fausse et revenait à chaque redémarrage. Elles ne se remplissent désormais que si le champ est vide, et se recalculent quand l'indicatif ou le locator change."
     ]
   },