feat(matrix): mark the slots already worked with the callsign in hand

The worked-before cell answered one question with two facts fused into it.
bandStatusCode takes the highest of them, so a confirmed entity outranks a
worked callsign — right for awards, wrong while chasing: a slot worked with the
DXpedition this morning reads "entity confirmed" and says nothing about it.

BandStatus now carries the callsign's own answer alongside the entity's, and the
cell draws a dot for it. The dot is deliberately identical everywhere — same
shape, same colour, over all five backgrounds — so it is read as one thing
rather than as five variants of the colour underneath it.

changelog.json

@@ -3,10 +3,12 @@
     "version": "0.26.20",
     "date": "",
     "en": [
-      "Each radio carries its own MY_RIG (Settings → CAT), written on every QSO made with it — ahead of the per-band station in Operating conditions, which says what you planned to use rather than which radio is keying. Left empty, nothing changes."
+      "Each radio carries its own MY_RIG (Settings → CAT), written on every QSO made with it — ahead of the per-band station in Operating conditions, which says what you planned to use rather than which radio is keying. Left empty, nothing changes.",
+      "Worked-before matrix: a dot in the corner of a cell now means the callsign you are working has already been worked on that slot, whatever colour the entity status gave the cell."
     ],
     "fr": [
-      "Chaque radio porte son propre MY_RIG (Réglages → CAT), inscrit sur chaque QSO fait avec elle — avant la station par bande des Conditions de trafic, qui dit ce qui était prévu et non quelle radio émet. Laissé vide, rien ne change."
+      "Chaque radio porte son propre MY_RIG (Réglages → CAT), inscrit sur chaque QSO fait avec elle — avant la station par bande des Conditions de trafic, qui dit ce qui était prévu et non quelle radio émet. Laissé vide, rien ne change.",
+      "Matrice des contacts : un point dans le coin d'une case indique que l'indicatif en cours a déjà été contacté sur ce créneau, quelle que soit la couleur donnée par le statut de l'entité."
     ]
   },
   {
@@ -1929,4 +1931,4 @@
       "Ce résumé « Nouveautés » s'affiche désormais au premier lancement après chaque mise à jour."
     ]
   }
-]
+]