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.

internal/qso/qso.go

@@ -1901,10 +1901,24 @@ type WorkedBefore struct {
 }
 
 // BandStatus is one cell in the worked-before grid.
+//
+// Status is the single highest thing true of the cell, which is what colours
+// it. Call is the SAME cell's answer to a different question — "have I worked
+// THIS callsign here" — kept separately because the two are asked at the same
+// moment and one was hiding the other.
+//
+// Chasing an expedition, an operator needs both: whether the slot is still
+// missing for the entity (does this fill a DXCC hole) and whether this
+// expedition has already been worked on it (would this be a dupe). A confirmed
+// entity outranks a worked callsign in Status — correctly, for awards — so a
+// slot worked with the DX yesterday can read "entity confirmed" and say nothing
+// at all about yesterday.
 type BandStatus struct {
 	Band   string `json:"band"`   // ADIF lowercase band, e.g. "20m"
 	Class  string `json:"class"`  // "PH" | "CW" | "DIG"
 	Status string `json:"status"` // "call_c" | "call_w" | "dxcc_c" | "dxcc_w"
+	// Call is "", "w" (worked with this callsign) or "c" (confirmed with it).
+	Call string `json:"call,omitempty"`
 }
 
 // Band-status codes, lowest first. The ORDER is the rule: a cell shows the
@@ -2243,6 +2257,8 @@ func (r *Repo) WorkedBefore(ctx context.Context, callsign string, dxccHint int,
 	}
 	type cellKey struct{ band, class string }
 	best := map[cellKey]int{}
+	// The call's own answer per cell, independent of the ladder above.
+	callByCell := map[cellKey]string{}
 	for statusRows.Next() {
 		var band, mode string
 		var callW, callC, dxccConfirmed int
@@ -2255,12 +2271,21 @@ func (r *Repo) WorkedBefore(ctx context.Context, callsign string, dxccHint int,
 		if cur, ok := best[k]; !ok || code > cur {
 			best[k] = code
 		}
+		// Confirmed beats worked here too, and neither is ever erased by the
+		// entity: this is only ever about the callsign.
+		switch {
+		case callC == 1:
+			callByCell[k] = "c"
+		case callW == 1 && callByCell[k] == "":
+			callByCell[k] = "w"
+		}
 	}
 	statusRows.Close()
 	codeStr := bandStatusNames
 	for k, code := range best {
 		wb.BandStatus = append(wb.BandStatus, BandStatus{
 			Band: k.band, Class: k.class, Status: codeStr[code],
+			Call: callByCell[k],
 		})
 	}
 	return wb, nil