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.

frontend/src/lib/i18n.tsx

@@ -127,6 +127,9 @@ const en: Dict = {
   'mx.tipCallConf': 'This callsign confirmed', 'mx.tipCallWork': 'This callsign worked (not confirmed)',
   'mx.tipDxConf': 'Entity confirmed (other callsign)', 'mx.tipDxWork': 'Entity worked (other callsign)',
   'mx.tipNone': 'Never worked', 'mx.tipClick': 'click to list the QSOs',
+  'mx.thisCall': 'this callsign',
+  'mx.tipThisCall': 'already worked with this callsign',
+  'mx.tipThisCallConf': 'already confirmed with this callsign',
   // FTx decodes panel (Tools -> FT decodes)
   'dec.tab': 'FT decodes', 'dec.title': 'Decodes', 'dec.cqOnly': 'CQ only',
   'dec.allBands': 'All bands', 'dec.allModes': 'All modes', 'toast.qsoLogged': 'QSO logged', 'dec.contsHint': 'Continents: click to keep one or several', 'dec.allConts': 'All continents',
@@ -613,6 +616,9 @@ const fr: Dict = {
   'mx.tipCallConf': 'Cet indicatif est confirmé', 'mx.tipCallWork': 'Cet indicatif est contacté (non confirmé)',
   'mx.tipDxConf': 'Entité confirmée (autre indicatif)', 'mx.tipDxWork': 'Entité contactée (autre indicatif)',
   'mx.tipNone': 'Jamais contacté', 'mx.tipClick': 'cliquer pour lister les QSO',
+  'mx.thisCall': 'cet indicatif',
+  'mx.tipThisCall': 'déjà contacté avec cet indicatif',
+  'mx.tipThisCallConf': 'déjà confirmé avec cet indicatif',
   // Panneau des decodes FTx (Outils -> Decodes FT)
   'dec.tab': 'Decodes FT', 'dec.title': 'Decodes', 'dec.cqOnly': 'CQ seulement',
   'dec.allBands': 'Toutes bandes', 'dec.allModes': 'Tous modes', 'toast.qsoLogged': 'QSO enregistré', 'dec.contsHint': 'Continents : clique pour en garder un ou plusieurs', 'dec.allConts': 'Tous continents',