fix: band change from OpsLog left the frequency on the old band

The log settled it: the backend was right all along. Every set produced
"readback +1.5s FreqA=21140000 Freq=21140000 -> shown 21140000" and published
cat:state with the new frequency and band. The display did not follow.

The fault is in the frontend. Changing band does two things at once: it opens the
1.5 s freeze that protects what the operator is typing, and it commands the rig.
The rig's answer comes back in ~170 ms — inside that freeze — and the handler
DROPPED any snapshot arriving during it. The backend only emits on change, so
nothing came afterwards, and the strip kept the old frequency until the VFO was
nudged. Changing band from the radio always worked because no freeze was open.

A dropped snapshot is now kept and replayed when the freeze closes, rather than
discarded. Further typing simply defers the replay again.

changelog.json

@@ -3,6 +3,7 @@
     "version": "0.21.9",
     "date": "2026-07-28",
     "en": [
+      "Changing band from OpsLog now updates the displayed frequency straight away. The rig moved, but its answer arrived inside the short grace window that protects what you are typing and was discarded — so the frequency stayed on the old band until you nudged the VFO.",
       "Bulk edit can now set the contacted station gridsquare, so a batch of QSOs imported without a locator can be corrected in one go.",
       "Filter builder: a confirmation date typed into a condition showed an empty box. The value was stored correctly, only the calendar field failed to display it.",
       "The Icom model list gains the IC-7300MKII (CI-V B6), plus the IC-7100, IC-7410, IC-7600 and IC-7851. The IC-7700 and IC-7800 were listed at the IC-7100's and IC-7410's addresses, so picking them set an address the rig never answers on.",
@@ -11,6 +12,7 @@
       "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": [
+      "Changer de bande depuis OpsLog met désormais la fréquence affichée à jour immédiatement. La radio se déplaçait bien, mais sa réponse arrivait pendant le court délai qui protège votre saisie et était ignorée — la fréquence restait donc sur l'ancienne bande jusqu'à ce qu'on touche le VFO.",
       "L'édition groupée peut désormais définir le locator de la station contactée : un lot de QSO importés sans locator se corrige en une fois.",
       "Constructeur de filtres : une date de confirmation saisie dans une condition s'affichait dans une case vide. La valeur était bien enregistrée, seul le champ calendrier ne la montrait pas.",
       "La liste des modèles Icom gagne l'IC-7300MKII (CI-V B6), ainsi que les IC-7100, IC-7410, IC-7600 et IC-7851. Les IC-7700 et IC-7800 y figuraient avec les adresses des IC-7100 et IC-7410 : les choisir réglait une adresse sur laquelle la radio ne répond jamais.",