feat(log): QSO number column, oldest contact = 1

Not the id: the primary key follows insertion order, so importing an old ADIF
gives the oldest contacts the highest ids. This is a rank over qso_date.

Computed over the WHOLE log, not the query result — ranking inside the result
would renumber every contact the moment a filter is applied, and QSO #1 would
change identity as the operator typed.

Held as one id-to-rank map, built from a single ordered id query and dropped
with the other derived indexes when the log changes. A contact logged from the
entry form is the newest, so it takes the next number without rereading the
log: AddQSO deliberately avoids full invalidation because a contest run would
pay for it once per QSO. A contact entered with an OLDER date belongs in the
middle of the order, so there the map is dropped and rebuilt rather than
mis-numbered.

changelog.json

@@ -7,14 +7,16 @@
       "New option \"Chase new grids\": locators learnt from your decodes and from PSK Reporter are kept in their own database, with their source.",
       "Band openings: the PSK Reporter feed is now filtered at the broker, which cuts it from about 83 messages a second to under two.",
       "Band openings: unticking a band now actually stops its announcements, and puts its badge out.",
-      "Callsign lookup: the website, postal code and HamQTH profile picture are now read — the QSO web column was never filled by any lookup."
+      "Callsign lookup: the website, postal code and HamQTH profile picture are now read — the QSO web column was never filled by any lookup.",
+      "New selectable column \"QSO number\": position in the log, 1 for the oldest contact."
     ],
     "fr": [
       "Cluster : le cache de locators garde 100 000 indicatifs et tourne au lieu de se vider, les locators ne disparaissent donc plus de la liste.",
       "Nouvelle option « Chasse aux nouveaux carrés » : les locators appris de tes décodes et de PSK Reporter sont conservés dans leur propre base, avec leur source.",
       "Ouvertures de bande : le flux PSK Reporter est désormais filtré chez le broker, ce qui le fait passer d environ 83 messages par seconde à moins de deux.",
       "Ouvertures de bande : décocher une bande arrête réellement ses annonces et éteint son badge.",
-      "Recherche d indicatif : le site web, le code postal et la photo de profil HamQTH sont désormais lus — la colonne web du QSO n était jamais remplie."
+      "Recherche d indicatif : le site web, le code postal et la photo de profil HamQTH sont désormais lus — la colonne web du QSO n était jamais remplie.",
+      "Nouvelle colonne sélectionnable « Numéro de QSO » : position dans le log, 1 pour le contact le plus ancien."
     ]
   },
   {